chore(plugin): bump to 0.1.21 for the planning-guidance edits

The two skills changed in 6eedb0f are shipped plugin content, and the
installer compares manifest versions to decide whether to refresh the cache
that actually executes. Without the bump the edits reach the repo and stop
there (#2209) — which is exactly the silent no-op the check exists to catch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

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, reusing-code), and your saved Scribe Processes auto-surfaced as skills (/scribe:sync). Replaces superpowers + file-memory with one app-backed plugin.",
-  "version": "0.1.20",
+  "version": "0.1.21",
   "author": { "name": "Bryan Van Deusen" },
   "mcpServers": {
     "scribe": {