CC 2.1.132 Adoption — Group A: foundation doc sweep

Four doc additions that document new CC behavior the rest of the codebase already relies on (matrix entries already shipped in v7.84.0). No functional code changes. Closes 4 cc-adoption issues filed by the cron pipeline.

Issues closed 4 / 19 in the milestone

Issue	Feature	CC	Category
#1639	enterworktree_branches_from_local_head	2.1.128	breaking
#1641	stale_installed_plugins_path_fix	2.1.128	breaking
#1644	ctrl_r_history_global_default	2.1.129	breaking
(no GH issue, gap_score=5)	auto_mode_classifier_error_hint	2.1.128	new_field

Files touched

Path	Change
src/skills/chain-patterns/references/worktree-agent-pattern.md	New "Branch base (CC 2.1.128+)" section — documents that EnterWorktree branches from local HEAD
src/skills/doctor/references/remediation-guide.md	Two new troubleshooting entries: stale plugin paths, auto-mode classifier hints
src/skills/setup/references/keybindings.md	New "CC built-in keys worth knowing" section — Ctrl+R global default, Ctrl+S to scope

Why doc-only is enough for Group A

All four features are upstream behavior changes that we already gate on via the floor (v7.84.0 raised it to 2.1.132). The matrix entries in cc-version-matrix.ts were added by PR #1623 and the doctor skill already surfaces version-pinned features. What was missing was the human-facing remediation/usage notes that let a maintainer or contributor understand the new behavior when they're reading skill references — not searching the matrix.

Before / after (worktree-agent-pattern.md)

Before

## Hooks That Fire
…

## Limitations
- Worktree agents are slightly slower
- Each worktree is a full copy
- Merge conflicts possible if agents
  edit same files
- Don't use for read-only agents

After

## Hooks That Fire
…

## Branch base (CC 2.1.128+)
EnterWorktree branches from local
HEAD, not origin/<default-branch>.
- Unpushed commits preserved
- No need to push first
- We floor at 2.1.132 — done.

## Limitations
…unchanged…

Verification

✅ npm run build regenerates plugins/ with the doc updates mirrored
✅ npm run test:skills — frontmatter + structure unchanged
✅ npm run typecheck — no source changed
✅ No counts moved (skills/agents/hooks unchanged)

Next groups (B–E) handle MCP hygiene, security-adjacent fixes, config behavior, and new distribution surfaces. See the per-group rationale in the chained roadmap.