chore: clean up plans — remove 23 implemented plans/specs

All older plans and specs have been implemented. Removed:

docs/superpowers/plans (8 files):
- 2026-04-07-audit-remaining-fixes (indexer util, incremental, shutdown)
- 2026-04-07-encrypted-sharing (src-tauri/src/share/)
- 2026-04-07-github-sync (src-tauri/src/sync/)
- 2026-04-07-sqlite-hardening (DB migrations, pool, queries)
- 2026-04-08-ai-intelligence (ai/, mcp/, RAG via memvid)
- 2026-04-08-blocknote-migration (implemented this session)
- 2026-04-08-inline-ai-editor (superseded by BlockNote version)
- 2026-04-09-inline-ai-prompt (implemented this session)

docs/superpowers/specs (3 files): matching design docs

docs/plans (6 files):
- 2026-04-05-tasks-calendar-keyboard
- 2026-04-06-executable-code-blocks
- 2026-04-06-layout-pass1-component-extraction
- 2026-04-06-midnight-tokyo-ui-overhaul
- 2026-04-06-properties-aliases-mentions
- 2026-04-06-theme-system

docs/specs (7 files): matching design docs

Kept only:
- docs/superpowers/plans/2026-04-09-fabric-patterns-integration.md
  (researched but not implemented — slash commands for /summarize,
  /improve, /extract-wisdom, etc.)

Empty dirs removed. All plan history remains in git.

Author: neur0map