Add PLAN.md rule, garage .gitignore, remove hardcoded server port hint

- AGENTS.md: mark PLAN.md as user-owned (never modify; it stays tracked)
- move the .env ignore rule to the garage root so it covers any depth
- drop the hardcoded "port 7654" hint from the no-server message; the target
  is now reported from the resolved SERVER_URL. The 7654 fallback remains
  only as the upstream TR default.

DevControlBot_garage/DevControlBot/DevControlBot.sh

@@ -67,7 +67,7 @@ export DEVCONTROLBOT_DEBUG="$BUILD_MODE"
 # The runBot task's shell always exits 0 (otherwise Nimble raises a NimScript
 # exception with a stack trace and a dump of the whole script) and writes the
 # bot's real exit code here instead. We read it back and exit with it, so
-# BotLauncher still sees the faithful status: 1 = no game server on 7654,
+# BotLauncher still sees the faithful status: 1 = no game server at SERVER_URL,
 # 2 = a dependency is missing, 3 = compile failure, anything else = the bot's
 # own code, 0 = clean run.
 STATUS_FILE="$(mktemp "${TMPDIR:-/tmp}/devcontrolbot.status.XXXXXX")"