chore(plans): close out plan 004 (already shipped in #70)

Plan 004's fix was independently implemented and merged in PR #70
(commit 9e2cfeb, 'fix(plugin-git): guard revisions against argument
injection'), matching the plan's spec exactly: isSafeRevision guard in
node/git.ts, --end-of-options + guard in log.ts and show.ts, and the
same injection-guard tests in git.test.ts. Verified: git plugin tests
(16/16), typecheck, and lint all pass clean. Marking the plan DONE and
removing the now-stale plan file.

Author: antfubot

plans/004-git-argument-injection.md

@@ -16,7 +16,7 @@ changes are allowed as long as they're marked).
 | 001 | Add missing `typecheck` scripts (inspect + 5 examples) | dx | P1 | S | — | DONE (partial — see note) |
 | 002 | Clear the critical `shell-quote` advisory in the bundle | security/deps | P1 | S | — | DONE |
 | 003 | Reject cross-origin WebSocket upgrades ⚠️ | security | P1 | S | — | DONE |
-| 004 | Stop git argument injection via `ref`/`hash` | security/bug | P1 | S | — | TODO |
+| 004 | Stop git argument injection via `ref`/`hash` | security/bug | P1 | S | — | DONE |
 | 005 | Don't cache a rejected RPC `setup()` promise | bug | P1 | S | — | DONE |
 | 006 | Bound `SharedState.syncIds` (memory leak) | bug | P1 | S | — | DONE |
 | 007 | Behavioral tests for the auth/OTP trust boundary | tests | P1 | S | — | DONE |