feat(scribe): snippet recording nudge — reusing-code skill + MCP/SessionStart guidance

Step 5 of the Drafter recall milestone (#227): teach agents the two
snippet reflexes — search recorded snippets before writing a new
helper/util/component, and record something reusable the moment it's
built — via the app's own instruction surfaces, not a Scribe rule
(project rule #119). All instance-agnostic (rule #115).

- plugin/skills/reusing-code/SKILL.md: new auto-surfacing process-skill
  covering both reflexes (recall-before-rebuild + record-when-reusable).
- src/scribe/mcp/server.py: a Snippets paragraph in the MCP _INSTRUCTIONS.
- plugin/hooks/scribe_static_context.md: a "reuse before rebuilding"
  bullet in the SessionStart static context.
- plugin/.claude-plugin/plugin.json: version 0.1.12 -> 0.1.13 in the same
  change so the autoUpdate marketplace ships it (the #1040 lesson);
  description skill list updated.
- plugin/README.md: trued the process-skill list to what actually ships.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pa2EsuB54BuWQ8GfJq9c7t

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
-  "description": "Scribe system-of-record 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": "0.1.12",
+  "description": "Scribe system-of-record 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, reusing-code), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
+  "version": "0.1.13",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {