docs(AGENT): require PLAN.md update on every wip + final commit

The "living document" rule was soft and got ignored — coders wrote
PLAN.md once at session start and then drifted away from it. Tie the
update to a trigger they already do (the wip/final commit), and call
out stale "Current state" as a process failure.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.huskies/AGENT.md

@@ -19,6 +19,8 @@ At the very start of each coder session, before doing any code exploration, chec
 
 `PLAN.md` is a living document. Update it after each completed AC or natural unit of work — not only at the start.
 
+**Required trigger:** Before every `wip(...)` commit AND the final commit, update PLAN.md's "Current state" section to reflect what's now done, and tick off completed items in "What's left". This is required, not optional — stale "Current state: No code changes yet" while files are being edited is a process failure. Stage the PLAN.md update in the same commit as the code change it describes.
+
 Required sections:
 
 ```markdown