feat: telegram listener pushes command list to bot menu via setMyCommands

Map entries may now carry a menu description (/cmd::desc=bash) shown in
the bot's "/" menu; it falls back to the bash command (~40 chars) when
omitted. The command list is pushed automatically after every map edit,
on --enable, and at daemon start, plus a manual --sync-commands flag
(wired into POS_FLAGS completion). Names are validated against Telegram's
lowercase [a-z0-9_] rule — invalid ones are skipped from the menu with a
warning but still resolve when typed; an empty map clears the menu.

Fixes found by unit-testing the sync path: map_has always returned false
(awk END{exit 1} overrode the match), map_set had a local cross-reference
that broke under set -u, and warn() leaked into the generated JSON (now
stderr). Docs + AGENT_TODO updated; make gen && make check pass.

DOC/AGENT_Context_Project.md

@@ -553,7 +553,7 @@ Use conventional prefixes: `feat:`, `fix:`, `docs:`, `refactor:`, `chore:`
 | `features/autostart.sh` | 14 | Boot-time feature (moved from `bin/`, flag-gated service) |
 <!-- GEN:START filetable -->
 | `bin/pos` | 270 | CLI dispatcher with smart arg matching + logging + category help |
-| `bin/pos-communication-telegram-listener` | 437 | Telegram bot listener: map /command → bash, run them on chat messages |
+| `bin/pos-communication-telegram-listener` | 508 | Telegram bot listener: map /command → bash, run them on chat messages |
 | `bin/pos-communication-telegram-sender` | 270 | Send Telegram messages/files/links/stickers via Bot API (send, test, config set) |
 | `bin/pos-config` | 80 | Interactive editor for the tools' runtime config (reads # POS_CONFIG: registry) |
 | `bin/pos-docker-compose` | 366 | Docker Compose service manager (ls/up/down/restart/logs/update/config) |