Add tarot readings, encrypted quote wall, display name resolution, and uptime reporting

New features:
- !tarot and !tarotspread commands with LLM-powered readings (zodiac-aware)
- !quote system with AES-256-GCM encryption at rest, reply-to-save, search, and quoteboard
- Shared crypto utility (internal/crypto) for AES-256-GCM encrypt/decrypt/HMAC
- ResolveUser now matches display names via room membership as fallback
- !vibe and !tldr show bot uptime when insufficient messages buffered

Bug fixes:
- Fix duplicate quotes table schema that would crash quotewall at runtime
- Fix biased random selection in quote retrieval (use rand.Intn)
- Fix XP rank calculation to handle tied scores with COUNT(DISTINCT xp)
- Scope all leaderboards to room members (repboard, pottyboard, insultboard, firstboard, rankings, emojiboard)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -44,6 +44,9 @@ MISSING_MAX_DAYS=90           # days after which they're considered gone, not mi
 MISSING_MIN_MESSAGES=10       # minimum lifetime messages to be eligible
 MISSING_EXCLUDE_USERS=        # comma-separated user IDs to never list as missing
 
+# ---- Encryption ----
+QUOTE_ENCRYPTION_KEY=         # Base64-encoded 32-byte AES-256 key (required for !quote)
+
 # ---- Rate Limits (per user per day) ----
 RATELIMIT_WEATHER=5
 RATELIMIT_TRANSLATE=20