Add co-op dungeon system (party runs, voting, betting, gifts, items)

Multi-day party runs with funding decisions, TwinBee-narrated floor events,
spectator parimutuel betting, basket/mimic gift system, and weighted-roll
item distribution including masterwork drops at T4-T5.

Schema (5 tables, 2 fewer than spec by computing helpfulness on-the-fly and
skipping the loot-pending state):
- coop_dungeon_runs / _members (daily funding as JSON column)
- coop_dungeon_events (votes as JSON, used to derive TwinBee helpfulness)
- coop_dungeon_bets / _gifts

Mechanics:
- 2-4 player parties, 24h invite window, locks consume one combat action
- Per-floor success roll: base + sum(funding) + level/pet bonuses + event
  vote modifier + active gift modifiers, clamped to 5..95
- Funding tiers (none/min/std/agg/all_in) with liability cap at +8% for
  under-leveled players
- TwinBee narrates events from existing flavor pool; 20 authored events with
  per-option modifiers and embedded recommendation
- Parimutuel betting with 10% rake; odds line shown on lock/daily/status posts
- Gift modifiers symmetric at 50/50 sender mix so no dominant strategy
- Item drops on success via weight-by-contribution roll; T4 25% / T5 100%
  masterwork chance (random pick from existing T4/T5 defs)

Balance via Monte Carlo (coop_dungeon_balance_test.go):
- All tiers exceed 1.5x solo daily income at average party profile
- Optimal funding strategy walks up tiers correctly (Min/Std/Std/Mixed/Agg)
- All-In stays -EV at every tier (boost lever, not optimal play)

Tests: parsing, liability cap, JSON roundtrips, vote tally with leader
tiebreak, event meta consistency, parimutuel payouts, gift EV symmetry,
weighted-roll distribution (Monte Carlo), masterwork tier gates.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/db/db.go

@@ -1373,6 +1373,75 @@ CREATE TABLE IF NOT EXISTS holdem_tip_audit (
 CREATE INDEX IF NOT EXISTS idx_tip_audit_user ON holdem_tip_audit(user_id);
 CREATE INDEX IF NOT EXISTS idx_tip_audit_action ON holdem_tip_audit(action, street);
 
+-- Co-op Dungeon (party multi-day runs)
+CREATE TABLE IF NOT EXISTS coop_dungeon_runs (
+    id              INTEGER PRIMARY KEY AUTOINCREMENT,
+    tier            INTEGER NOT NULL,
+    status          TEXT NOT NULL DEFAULT 'open',  -- open, active, complete, wiped, cancelled
+    leader_id       TEXT NOT NULL,
+    current_day     INTEGER NOT NULL DEFAULT 0,
+    total_days      INTEGER NOT NULL,
+    base_difficulty INTEGER NOT NULL,              -- per-floor failure % at zero modifier
+    gold_pool       INTEGER NOT NULL DEFAULT 0,    -- accumulated funding
+    reward_total    INTEGER NOT NULL DEFAULT 0,    -- final reward (set on completion)
+    created_at      DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    locked_at       DATETIME,
+    completed_at    DATETIME
+);
+CREATE INDEX IF NOT EXISTS idx_coop_runs_status ON coop_dungeon_runs(status);
+
+CREATE TABLE IF NOT EXISTS coop_dungeon_members (
+    run_id            INTEGER NOT NULL,
+    user_id           TEXT NOT NULL,
+    turn_order        INTEGER NOT NULL,
+    total_contributed INTEGER NOT NULL DEFAULT 0,
+    is_liability      INTEGER NOT NULL DEFAULT 0,
+    daily_funding     TEXT NOT NULL DEFAULT '{}',  -- JSON: {"1":"standard","2":"all_in",...}
+    PRIMARY KEY (run_id, user_id)
+);
+CREATE INDEX IF NOT EXISTS idx_coop_members_user ON coop_dungeon_members(user_id);
+
+CREATE TABLE IF NOT EXISTS coop_dungeon_events (
+    run_id           INTEGER NOT NULL,
+    day              INTEGER NOT NULL,
+    category         TEXT NOT NULL,                  -- obstacle, opportunity, crisis, encounter
+    event_index      INTEGER NOT NULL,               -- index into the category flavor pool
+    recommended      TEXT NOT NULL,                  -- A, B, or C — TwinBee's pick
+    votes            TEXT NOT NULL DEFAULT '{}',     -- JSON {"@user:host": "A"}
+    winning_vote     TEXT DEFAULT NULL,
+    outcome          TEXT DEFAULT NULL,              -- 'success' or 'failure' (after resolution)
+    modifier_applied INTEGER DEFAULT 0,
+    post_event_id    TEXT DEFAULT NULL,              -- Matrix event ID for live edit
+    PRIMARY KEY (run_id, day)
+);
+CREATE INDEX IF NOT EXISTS idx_coop_events_outcome ON coop_dungeon_events(outcome);
+
+CREATE TABLE IF NOT EXISTS coop_dungeon_bets (
+    run_id     INTEGER NOT NULL,
+    player_id  TEXT NOT NULL,
+    position   TEXT NOT NULL,                 -- 'success' or 'failure'
+    amount     INTEGER NOT NULL,
+    placed_at  DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    payout     INTEGER,                       -- NULL until run resolves
+    PRIMARY KEY (run_id, player_id)
+);
+CREATE INDEX IF NOT EXISTS idx_coop_bets_run ON coop_dungeon_bets(run_id);
+
+CREATE TABLE IF NOT EXISTS coop_dungeon_gifts (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    run_id        INTEGER NOT NULL,
+    sender_id     TEXT NOT NULL,
+    day           INTEGER NOT NULL,
+    gift_type     TEXT NOT NULL,                 -- 'basket' or 'mimic'
+    votes         TEXT NOT NULL DEFAULT '{}',    -- JSON {"@user:host": "open"|"leave"}
+    vote_result   TEXT,                          -- 'opened' or 'left'
+    outcome       TEXT,                          -- 'boost' or 'reduction'
+    modifier      INTEGER NOT NULL DEFAULT 0,
+    post_event_id TEXT,
+    sent_at       DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    resolved_at   DATETIME
+);
+CREATE INDEX IF NOT EXISTS idx_coop_gifts_run_day ON coop_dungeon_gifts(run_id, day, vote_result);
 `
 
 // SeedSchedulerDefaults inserts default scheduler jobs if they don't exist.