feat: telegram listener text-prefix map — <word> <text> routes to a mapped app

Generalizes the Telegram listener with a configurable text-prefix map
(telegram_prefixes.env): any non-command message '<word> <text>' runs
the mapped command with <text> appended as ONE quoted argument — e.g.
opencode=opencode turns 'opencode check cpu' into opencode "check cpu".

Routing order per message: text-prefix map → built-in Gemini ai bridge →
/command map → Unknown command. A mapped word shadows the Gemini bridge.

The prefix verb is reworked: bare = list map + bridge word; 'prefix
<word> <cmd...>' = map; 'prefix <word>' = show; 'prefix -r <word>' = remove.
The Gemini trigger word itself is now set via 'pos config telegram'
(TELEGRAM_AI_PREFIX).

Also extracted run_and_reply() to share the /command-map (60s) and
prefix (120s) execution semantics; fixed a latent set -e abort on
invalid templates in prefix_map_set's check_syntax call.

Verified: 27/27 routing-harness assertions, full CLI verb suite,
dispatch smoke, pos config telegram render, bash -n, make gen && make check,
make lint 0 FAIL / 0 WARN, shellcheck -S style (0 new findings).

bin/pos-communication-telegram-listener

@@ -281,7 +281,7 @@ prefix_map_find() {
         cmd="${line#*=}"
         word="${word# }"
         cmd="${cmd# }"
-        [ -n "$word" ] && [ -n "$cmd" ] || continue
+        [[ -n "$word" && -n "$cmd" ]] || continue
         if [[ "$text" =~ ^"$word"[[:space:]](.*)$ ]]; then
             rem="${BASH_REMATCH[1]}"
             [ -n "$rem" ] || continue