Rework /scoped-models command UX

- Renamed from /models to /scoped-models
- Changes are now session-only by default (Ctrl+S to persist to settings)
- Added search with fuzzy filtering
- Hotkeys: Enter toggle, Ctrl+A enable all, Ctrl+X clear all, Ctrl+P toggle provider
- Ctrl+C clears search (or exits if empty), Escape exits
- Enabled models shown at top of list
- No checkmarks when all models enabled (no scope)
- First toggle when unscoped clears all and selects that model
- Uses current session thinking level instead of settings default
- Reads from session state first (preserves session-only changes across /scoped-models invocations)

Builds on #626

packages/coding-agent/README.md

@@ -236,7 +236,7 @@ The agent reads, writes, and edits files, and executes commands via bash.
 |---------|-------------|
 | `/settings` | Open settings menu (thinking, theme, message delivery modes, toggles) |
 | `/model` | Switch models mid-session. Use `/model <search>` or `provider/model` to prefilter/disambiguate. |
-| `/models` | Enable/disable models for Ctrl+P cycling |
+| `/scoped-models` | Enable/disable models for Ctrl+P cycling |
 | `/export [file]` | Export session to self-contained HTML |
 | `/share` | Upload session as secret GitHub gist, get shareable URL (requires `gh` CLI) |
 | `/session` | Show session info: path, message counts, token usage, cost |