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.
Problem: forge.nvim silently ignored unsupported features on
non-GitHub forges. Codeberg `pr_for_branch_cmd` blocked all PR
creation, CI picker had zero actions, `repo_info` was hardcoded,
and the compose buffer showed draft/reviewer fields that did nothing.
Solution: add `forge.Capabilities` declaration (`draft`, `reviewers`,
`per_pr_checks`, `ci_json`) to each source. Compose buffer hides
unsupported fields. Per-PR checks falls back to repo-wide CI with
a notification. Fix Codeberg `pr_for_branch_cmd` to filter by branch
via jq, implement `repo_info` and `list_runs_json_cmd` via Gitea API,
add `default_branch_cmd` fallback, and add yank notifications for
GitLab/Codeberg.
