fix: make bot startup resilient (self-healing state, gated cogs, loud failures)

Container/native startup died silently on any missing file/service. Now:

constants.py - self-healing runtime layout at import:
- create missing dirs (log dir, LOGSTORE, GRAPHICS_PATH, MUSIC_FOLDER)
- seed missing state files from the repo templates shipped next to
  constants.py (settings/system_gpt/pamiec/pamiec_muzyki/accident_log),
  falling back to safe empty JSON; existing files are NEVER overwritten

bot.py:
- log to stdout too, so 'docker logs' finally shows the crash reason
- missing Discord token = loud sys.exit with mount/env instructions
  (was: silent return -> container crash-loop with empty logs)
- every cog loads independently (one broken cog = skipped with traceback,
  bot continues)
- musician/librarian cogs are health-gated: enabled only when the service
  answers HTTP; a watchdog re-checks every 5 min and enables them the
  moment the service comes alive (no restart needed); tree re-synced
- on_ready reconnects no longer re-load extensions

requirements_conan.txt + Dockerfile.bot: aiomcrcon (Python <=3.11 only)
moved to best-effort extras so the 3.13 image builds clean and the
conanjurer cog stays dormant without it.

DOCKER_PROXMOX.md: startup model (core vs gated cogs) + crash-loop
troubleshooting incl. the 'disappearing files' checklist (nothing in the
stack deletes host files; bind mount = live state).

Verified: fresh-volume seeding creates dirs+templates, existing files
untouched, missing-token exits with FATAL message, health-gating logic
(stub-based runpy tests).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

requirements_conan.txt

@@ -0,0 +1,6 @@
+# Optional extras for the Conan Exiles bridge (conanjurer cog).
+#
+# aiomcrcon currently installs only on Python <= 3.11, while the main image
+# runs 3.13. Install is therefore best-effort: when it fails the conanjurer
+# cog simply stays dormant (its imports are guarded) and the bot runs fine.
+aiomcrcon