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.nimble

@@ -25,7 +25,7 @@ requires "jsony >= 1.1.5"
 #
 # `exec` turns ANY non-zero exit into a NimScript exception, which prints a
 # stack trace plus an escaped copy of the whole script. That is nonsense for the
-# expected "no game server on 7654" outcome. So the shell always exits 0 and
+# expected "no game server at SERVER_URL" outcome. So the shell always exits 0 and
 # hands the real code back through the file named by $DEVCONTROLBOT_STATUS_FILE,
 # which DevControlBot.sh exports and then re-exits with. Direct `nimble runBot`
 # (no such variable) keeps the old behaviour: the shell exits with the real code
@@ -216,7 +216,7 @@ if [ $bot_rc -ne 0 ]; then
     # The Tank Royale client answers a refused connection with this exact
     # exit code, so it means "no server", not "broken bot".
     echo "[devcontrolbot] No game server on ${SERVER_URL:-ws://localhost:7654} (SERVER_URL)." >&2
-    echo "[devcontrolbot] Start the Tank Royale server, or check it is listening on port 7654." >&2
+    echo "[devcontrolbot] Start the Tank Royale server, or point SERVER_URL at a running one." >&2
   else
     echo "[devcontrolbot] The bot ran but failed at runtime (crash or bad metadata)." >&2
   fi