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/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
-  "description": "Scribe second brain for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, and a set of process-skills (writing-plans, systematic-debugging, verification, brainstorming). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.7",
+  "description": "Scribe second brain for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, process-skills (writing-plans, systematic-debugging, verification, brainstorming), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
+  "version": "0.1.8",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {