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>

src/scribe/routes/plugin.py

@@ -57,6 +57,20 @@ async def session_context():
     return jsonify(result)
 
 
+@plugin_bp.get("/processes")
+@login_required
+async def process_manifest():
+    """Stored Processes as skill-stub specs for the plugin's sync script.
+
+    The plugin's `scribe_sync_processes.sh` (run at SessionStart and via the
+    `/scribe:sync` command) curls this and writes one auto-surfacing local skill
+    per Process into ~/.claude/skills/. See services/plugin_context.
+    build_process_manifest. A read-scoped API key suffices.
+    """
+    result = await plugin_ctx_svc.build_process_manifest(g.user.id)
+    return jsonify(result)
+
+
 @plugin_bp.get("/marketplace-url")
 @login_required
 async def get_marketplace_url():