chore: untrack planning & brainstorm docs, keep them local-only

Planning and brainstorm documents are working notes that should never be
committed (same philosophy as CLAUDE.md). Untrack the existing ones (kept
on disk locally via --cached) and gitignore docs/plans/, docs/brainstorms/,
and the stray docs/feat-gaming-optimize-plan.md execution-plan doc so they
can't be re-added.

The *POWER-PLANS* docs (docs/CPU-AWARE-POWER-PLANS.md, wiki/CPU-Power-Plans.md)
are feature reference docs, not project plans, and stay tracked.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: carterscode

.gitignore

@@ -28,3 +28,9 @@ CLAUDE.md
 
 # Personal scratch note — local only, never commit.
 qc
+
+# Planning & brainstorm docs are local-only working notes — never committed
+# (same philosophy as CLAUDE.md). Committed human docs live elsewhere in docs/.
+docs/plans/
+docs/brainstorms/
+docs/feat-gaming-optimize-plan.md