fix(discord-bridge): plafonul de cost e optional (COST_CAP_USD_DAY=off)

Costul raportat de CLI e pretul echivalent la API; pe abonament nu se
factureaza, deci plafonul zilnic oprea puntea fara motiv (5.71 / 5.00 USD).

- limits.parse_cap(): `off`/`none`/`nelimitat`/`0`/gol/gunoi => fara plafon
- stopped()/record_cost() nu mai opresc si nu mai alerteaza cand e dezactivat
- implicit devine `off`; /status arata „(fara plafon)"
- dashboard: /api/status si doctor nu mai crapa pe valoare ne-numerica
- README + ops/env.example explica de ce ramane off pe abonament

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B29CApsP1JkSdjYaGaHpE7

proxmox/lxc171-claude-agent/discord-bridge/bot.py

@@ -609,7 +609,8 @@ class Bridge:
             f"in coada   : {'da' if self.limits.queued(thread_id) else 'nu'}",
             f"procese    : {self.runner.live_count()} vii, {self.limits.free_slots} sloturi libere",
             f"cost fir   : ${float(rec.get('cost_usd_total') or 0.0):.4f}",
-            f"cost azi   : ${self.limits.cost_today():.4f} / ${cap:.2f}"
+            f"cost azi   : ${self.limits.cost_today():.4f}"
+            + (f" / ${cap:.2f}" if self.limits.cap_enabled else " (fara plafon)")
             + ("  ⛔ PLAFON ATINS" if self.limits.stopped() else ""),
             "```",
         ]