chore(release): v2.5.0 — drift-monitor family

[tigers1997]

Summary

Bundle release. Promotes the ## Unreleased block to ## [2.5.0] — 2026-05-21 and adds a "v2.5.0 — drift-monitor family" subsection that frames the four bundled PRs around the new drift-monitor primitive.

Headline pair (the drift-monitor family):

• feat: MCP drift monitor (manifest + SessionStart hook + /verify-setup rewrite) #51 — MCP drift monitor (introduced the pattern: baseline file + SessionStart hook + /verify-setup narrative)
• feat: stack-alignment monitor (manifest v2 + stack/command drift) #54 — Stack-alignment monitor (extended the pattern with stack-manifest drift + check-command alignment)

Housekeeping:

• docs: drop legacy /brainstorm references after superpowers v5.1.0 #49 — Drop legacy /brainstorm references after superpowers v5.1.0
• chore(compat): survey CC 2.1.133-2.1.146; track SchemaStore PR #5706 #52 — Survey CC 2.1.133–2.1.146 / track SchemaStore PR #5706 (no template changes; tested_up_to bump deferred)

CC_VERSION is already at 2.5.0 (set in earlier work).

Test plan

• CHANGELOG structure renders cleanly (## Unreleased empty, ## [2.5.0] populated, ## [2.4.0] unchanged)
• All 28 tests still pass on this branch (no code changes, sanity-check only)
• CI green