Add moderation system with deterministic detection and strike ladder

Deterministic-only detection (no LLM): word list with precompiled
leetspeak variation matching, text/image flood, wall of text, repeated
messages (Levenshtein similarity), mention flooding, link rate limiting
for new members, invite flooding, join/leave cycling detection.

Three-strike response ladder: warn + redact → temp mute → permanent ban.
Strikes expire after configurable period. Admin room notifications with
context cards. DMs over public callouts.

Admin commands: !mod warn/mute/unmute/ban/strikes/forgive/history/reload/
status/test. All require ADMIN_USERS membership.

Feature-flagged: disabled by default, set FEATURE_MODERATION=true to
enable. All thresholds configurable via env vars. New member grace
period with stricter thresholds. Word list hot-reload via !mod reload.

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

.env.example

@@ -50,6 +50,34 @@ MISSING_EXCLUDE_USERS=        # comma-separated user IDs to never list as missin
 # ---- Encryption ----
 QUOTE_ENCRYPTION_KEY=         # Base64-encoded 32-byte AES-256 key (required for !quote)
 
+# ---- Moderation (disabled by default) ----
+FEATURE_MODERATION=            # set to "true" to enable the moderation system
+MOD_WORDLIST=                  # path to newline-delimited word list file
+MOD_WORDLIST_VARIATIONS=true   # check leetspeak/spaced variants
+MOD_STRIKE_EXPIRY_DAYS=30      # strikes expire after N days
+MOD_MUTE_DURATION_MINUTES=60   # temp mute duration on strike 2
+MOD_MAX_STRIKES=3              # strikes before permanent ban
+MOD_FLOOD_MESSAGE_COUNT=5      # messages within window = flood
+MOD_FLOOD_MESSAGE_WINDOW_SECONDS=10
+MOD_FLOOD_IMAGE_COUNT=3        # images/files within window = flood
+MOD_FLOOD_IMAGE_WINDOW_SECONDS=30
+MOD_MAX_MESSAGE_LENGTH=2000    # max chars per message (0 = disabled)
+MOD_REPEAT_COUNT=3             # same message N times = strike
+MOD_REPEAT_WINDOW_SECONDS=60
+MOD_REPEAT_SIMILARITY_THRESHOLD=0.85
+MOD_MENTION_MAX=5              # max unique @mentions per message
+MOD_MENTION_FLOOD_COUNT=3
+MOD_MENTION_FLOOD_WINDOW_SECONDS=30
+MOD_LINK_RATE_NEW_MEMBER=3     # max links per window (new members only)
+MOD_LINK_RATE_WINDOW_SECONDS=60
+MOD_INVITE_MAX_PER_HOUR=5
+MOD_JOIN_LEAVE_COUNT=3         # join/leave cycles = flag (no auto-strike)
+MOD_JOIN_LEAVE_WINDOW_MINUTES=10
+MOD_NEW_MEMBER_DAYS=14         # accounts newer than N days = stricter thresholds
+MOD_NEW_MEMBER_FLOOD_MULTIPLIER=0.5
+MOD_ADMIN_ROOM=                # dedicated admin room for mod notifications
+MOD_DM_ON_ACTION=true          # DM users when action is taken
+
 # ---- Rate Limits (per user per day) ----
 RATELIMIT_WEATHER=5
 RATELIMIT_TRANSLATE=20