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/AGENTS.md

@@ -18,6 +18,18 @@
 > is **NOT a layout contract for this folder**. If the root template and this file
 > disagree about layout, **this file wins.**
 
+> ## ⚠️ DO NOT TOUCH `PLAN.md`
+>
+> **[`PLAN.md`](PLAN.md) is the user's personal working notes file.** The user
+> maintains it and edits it exclusively.
+>
+> - Agents must **NEVER** modify, rewrite, reformat, move, delete or commit
+>   changes to `PLAN.md` — unless the user explicitly asks in that conversation.
+> - Reading it is **not** assumed or expected; do not open it by default.
+> - It **IS** tracked in git and is intended to be committed (deliberately added
+>   in commit `59fad00b`). Do **NOT** gitignore it and do **NOT**
+>   `git rm --cached` it.
+
 ## Start here
 
 This file is the working rules for the bot. The human-facing description lives in
@@ -103,7 +115,7 @@ forwards args and signals to `nimble runBot`, and propagates the exit code.
   directory containing the `.nimble`. From `DevControlBot_garage/` it fails with
   `Could not find a file with a .nimble extension inside the specified directory`.
 - `compile`/`build` are reserved Nimble builtin names — hence `runBot`.
-- Without a Tank Royale server on `ws://localhost:7654` the run fails with
+- Without a Tank Royale server at `SERVER_URL` the run fails with
   `[start] Cannot connect ... Connection refused` and exit code 1. That is
   expected during local verification, not a bug.
 
@@ -154,7 +166,7 @@ forwards args and signals to `nimble runBot`, and propagates the exit code.
   re-exits with the code. Never mask it to 0, never let the shell's code be
   swallowed.
 - Exit codes (keep them distinct, they are what BotLauncher branches on):
-  `0` clean, `1` no game server on 7654 (expected), `2` dependency not
+  `0` clean, `1` no game server at `SERVER_URL` (expected), `2` dependency not
   installed, `3` compile failure, anything else = the bot's own code.
   Each prints its own short, actionable line; compile failures keep the raw
   compiler errors.