feat(picker): add multi-backend picker abstraction

Problem: all pickers were tightly coupled to fzf-lua via ANSI strings
and fzf-specific action tables, making it impossible to use telescope
or snacks.nvim.

Solution: introduce `forge.picker` dispatcher with `fzf`, `telescope`,
and `snacks` backends. Format functions now return `forge.Segment[]`
instead of ANSI strings. `pickers.lua` builds backend-agnostic
`forge.PickerEntry[]` and delegates to `forge.picker.pick()`. Backend
auto-detection tries fzf-lua, snacks, telescope in order. Commits,
branches, and worktree pickers remain fzf-only with graceful fallback.

lua/forge/picker/fzf.lua

@@ -0,0 +1,76 @@
+local M = {}
+
+local fzf_args = (vim.env.FZF_DEFAULT_OPTS or '')
+  :gsub('%-%-bind=[^%s]+', '')
+  :gsub('%-%-color=[^%s]+', '')
+
+---@param key string
+---@return string
+local function to_fzf_key(key)
+  if key == '<cr>' then
+    return 'default'
+  end
+  local result = key:gsub('<c%-(%a)>', function(ch)
+    return 'ctrl-' .. ch:lower()
+  end)
+  return result
+end
+
+---@param segments forge.Segment[]
+---@return string
+local function render(segments)
+  local utils = require('fzf-lua.utils')
+  local parts = {}
+  for _, seg in ipairs(segments) do
+    if seg[2] then
+      table.insert(parts, utils.ansi_from_hl(seg[2], seg[1]))
+    else
+      table.insert(parts, seg[1])
+    end
+  end
+  return table.concat(parts)
+end
+
+---@param opts forge.PickerOpts
+function M.pick(opts)
+  local cfg = require('forge').config()
+  local keys = cfg.keys
+  if keys == false then
+    keys = {}
+  end
+  local bindings = keys[opts.picker_name] or {}
+
+  local lines = {}
+  for i, entry in ipairs(opts.entries) do
+    lines[i] = ('%d\t%s'):format(i, render(entry.display))
+  end
+
+  local fzf_actions = {}
+  for _, def in ipairs(opts.actions) do
+    local key = def.name == 'default' and '<cr>' or bindings[def.name]
+    if key then
+      fzf_actions[to_fzf_key(key)] = function(selected)
+        if not selected[1] then
+          def.fn(nil)
+          return
+        end
+        local idx = tonumber(selected[1]:match('^(%d+)'))
+        def.fn(idx and opts.entries[idx] or nil)
+      end
+    end
+  end
+
+  require('fzf-lua').fzf_exec(lines, {
+    fzf_args = fzf_args,
+    prompt = opts.prompt or '',
+    fzf_opts = {
+      ['--ansi'] = '',
+      ['--no-multi'] = '',
+      ['--with-nth'] = '2..',
+      ['--delimiter'] = '\t',
+    },
+    actions = fzf_actions,
+  })
+end
+
+return M

lua/forge/picker/init.lua

@@ -0,0 +1,80 @@
+local M = {}
+
+---@alias forge.Segment {[1]: string, [2]: string?}
+
+---@class forge.PickerEntry
+---@field display forge.Segment[]
+---@field value any
+---@field ordinal string?
+
+---@class forge.PickerActionDef
+---@field name string
+---@field fn fun(entry: forge.PickerEntry?)
+
+---@class forge.PickerOpts
+---@field prompt string?
+---@field entries forge.PickerEntry[]
+---@field actions forge.PickerActionDef[]
+---@field picker_name string
+
+---@type table<string, string>
+local backends = {
+  ['fzf-lua'] = 'forge.picker.fzf',
+  telescope = 'forge.picker.telescope',
+  snacks = 'forge.picker.snacks',
+}
+
+---@return string
+local function detect()
+  local cfg = require('forge').config()
+  local name = cfg.picker or 'auto'
+  if name ~= 'auto' then
+    return name
+  end
+  if pcall(require, 'fzf-lua') then
+    return 'fzf-lua'
+  end
+  if pcall(require, 'snacks') then
+    return 'snacks'
+  end
+  if pcall(require, 'telescope') then
+    return 'telescope'
+  end
+  return 'fzf-lua'
+end
+
+---@param entry forge.PickerEntry
+---@return string
+function M.ordinal(entry)
+  if entry.ordinal then
+    return entry.ordinal
+  end
+  local parts = {}
+  for _, seg in ipairs(entry.display) do
+    table.insert(parts, seg[1])
+  end
+  return table.concat(parts)
+end
+
+---@return string
+function M.backend()
+  return detect()
+end
+
+---@param opts forge.PickerOpts
+function M.pick(opts)
+  local name = detect()
+  local mod_path = backends[name]
+  if not mod_path then
+    vim.notify('[forge]: unknown picker backend: ' .. name, vim.log.levels.ERROR)
+    return
+  end
+  local ok, backend = pcall(require, mod_path)
+  if not ok then
+    vim.notify('[forge]: picker backend ' .. name .. ' not available', vim.log.levels.ERROR)
+    return
+  end
+  backend.pick(opts)
+end
+
+return M

lua/forge/picker/snacks.lua

@@ -0,0 +1,64 @@
+local M = {}
+
+---@param opts forge.PickerOpts
+function M.pick(opts)
+  local Snacks = require('snacks')
+  local picker_mod = require('forge.picker')
+
+  local cfg = require('forge').config()
+  local keys = cfg.keys
+  if keys == false then
+    keys = {}
+  end
+  local bindings = keys[opts.picker_name] or {}
+
+  local items = {}
+  for i, entry in ipairs(opts.entries) do
+    items[i] = {
+      idx = i,
+      text = picker_mod.ordinal(entry),
+      value = entry,
+    }
+  end
+
+  local snacks_actions = {}
+  local input_keys = {}
+  local list_keys = {}
+  for _, def in ipairs(opts.actions) do
+    local key = def.name == 'default' and '<cr>' or bindings[def.name]
+    if key then
+      local action_name = 'forge_' .. def.name
+      snacks_actions[action_name] = function(picker)
+        local item = picker:current()
+        picker:close()
+        def.fn(item and item.value or nil)
+      end
+      if key == '<cr>' then
+        snacks_actions['confirm'] = snacks_actions[action_name]
+      else
+        -- selene: allow(mixed_table)
+        input_keys[key] = { action_name, mode = { 'i', 'n' } }
+        list_keys[key] = action_name
+      end
+    end
+  end
+
+  Snacks.picker({
+    items = items,
+    prompt = opts.prompt,
+    format = function(item)
+      local ret = {}
+      for _, seg in ipairs(item.value.display) do
+        table.insert(ret, { seg[1], seg[2] or 'Normal' })
+      end
+      return ret
+    end,
+    actions = snacks_actions,
+    win = {
+      input = { keys = input_keys },
+      list = { keys = list_keys },
+    },
+  })
+end
+
+return M

lua/forge/picker/telescope.lua

@@ -0,0 +1,69 @@
+local M = {}
+
+---@param opts forge.PickerOpts
+function M.pick(opts)
+  local pickers = require('telescope.pickers')
+  local finders = require('telescope.finders')
+  local conf = require('telescope.config').values
+  local actions = require('telescope.actions')
+  local action_state = require('telescope.actions.state')
+  local picker_mod = require('forge.picker')
+
+  local cfg = require('forge').config()
+  local keys = cfg.keys
+  if keys == false then
+    keys = {}
+  end
+  local bindings = keys[opts.picker_name] or {}
+
+  local finder = finders.new_table({
+    results = opts.entries,
+    entry_maker = function(entry)
+      return {
+        value = entry,
+        ordinal = picker_mod.ordinal(entry),
+        display = function(tbl)
+          local text = ''
+          local hl_list = {}
+          for _, seg in ipairs(tbl.value.display) do
+            local start = #text
+            text = text .. seg[1]
+            if seg[2] then
+              table.insert(hl_list, { { start, #text }, seg[2] })
+            end
+          end
+          return text, hl_list
+        end,
+      }
+    end,
+  })
+
+  pickers
+    .new({}, {
+      prompt_title = (opts.prompt or ''):gsub('[>%s]+$', ''),
+      finder = finder,
+      sorter = conf.generic_sorter({}),
+      attach_mappings = function(prompt_bufnr, map)
+        for _, def in ipairs(opts.actions) do
+          local key = def.name == 'default' and '<cr>' or bindings[def.name]
+          if key then
+            local function action_fn()
+              local entry = action_state.get_selected_entry()
+              actions.close(prompt_bufnr)
+              def.fn(entry and entry.value or nil)
+            end
+            if key == '<cr>' then
+              actions.select_default:replace(action_fn)
+            else
+              map('i', key, action_fn)
+              map('n', key, action_fn)
+            end
+          end
+        end
+        return true
+      end,
+    })
+    :find()
+end
+
+return M