feat(plugin): Phase 4 — Scribe Processes auto-surface as local skills

#755 Phase 4. Saved Scribe Processes (DRY pass, Drift Audit, …) now surface as
auto-triggered Claude Code skills instead of pull-only get_process calls.

Design correction vs the plan: stubs live in the USER's ~/.claude/skills/, NOT
plugin/skills/_instance/. The plugin is git-cloned and identical per install, so
instance-specific generated files can't ride in it; personal skills are
live-detected within the session (verified via claude-code-guide). MCP prompts
were the alternative but are pull-only (no relevance auto-surface), so skills are
the right primitive.

- backend: GET /api/plugin/processes manifest (services/plugin_context.
  build_process_manifest) — {name, slug, description} per Process; description is
  the auto-surface trigger (title + preview); slugs deduped, blanks skipped.
- plugin: scribe_sync_processes.sh writes ~/.claude/skills/scribe-proc-<slug>/
  SKILL.md (body = "call get_process(name), follow verbatim") and PRUNES stale
  scribe-proc-* stubs. Fail-open + silent; a transient fetch failure never wipes
  existing stubs. Runs as a 2nd SessionStart hook + via the /scribe:sync command.
- plugin.json 0.1.7 → 0.1.8; README updated.
- tests: build_process_manifest (render, slug dedupe, blank-title skip, preview
  truncation). Sync script's write+prune validated in isolation (plugin/** is not
  CI-covered): correct stubs created, stale pruned, unrelated skills untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugin/commands/sync.md

@@ -0,0 +1,20 @@
+---
+description: Sync your Scribe stored Processes into auto-surfacing local skills
+allowed-tools: Bash(bash:*), Bash(ls:*)
+---
+
+Regenerate the local skill stubs for your Scribe **Processes** so they auto-surface
+this session. Each Process becomes a `~/.claude/skills/scribe-proc-<slug>/SKILL.md`
+whose body calls `get_process(<name>)` for the live procedure.
+
+This normally runs automatically at session start; use it after adding or editing
+a Process when you want it available immediately (Claude Code live-detects the new
+skill files within this session — no restart needed).
+
+Run the bundled sync script, then list what was synced:
+
+```
+bash "${CLAUDE_PLUGIN_ROOT}/hooks/scribe_sync_processes.sh" && ls ~/.claude/skills 2>/dev/null | grep '^scribe-proc-' || echo "no Scribe process skills (no Processes, or Scribe unreachable)"
+```
+
+Report which `scribe-proc-*` skills are now present.