Schema: games, campaign_members, signups (campaign forming), audit_log; full campaigns columns

Fill out the domain for many campaigns.

- [ ] `games` — name, min/max players, default duration; referenced by campaigns and (later) single game days.
- [ ] `campaigns` gains: `recurrence_anchor` + `interval_weeks`, quorum, capacity, `max_sessions`, **`first_session_number`** (session numbers need seeding because history starts empty), lifecycle state.
- [ ] `campaign_members` — the roster: campaign_id, user_id, role (gm/player), joined_at, character_name.
- [ ] `signups` — target_type (`campaign_forming` now; `game_day` in phase 5), target_id, user_id, state, position, character_name — with the **CHECK constraint that a signup never targets a session**.
- [ ] `audit_log` — who changed what from the console.