feat: support co-gm group delegation

src/GmRelay.Bot/Migrations/V008__add_group_managers.sql

@@ -0,0 +1,26 @@
+-- Add explicit owner/co-GM management roles for each Telegram group.
+
+INSERT INTO players (telegram_id, display_name)
+SELECT DISTINCT gg.gm_telegram_id,
+       'GM ' || gg.gm_telegram_id::text
+FROM game_groups gg
+ON CONFLICT (telegram_id) DO NOTHING;
+
+CREATE TABLE group_managers (
+    id                  UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    group_id            UUID NOT NULL REFERENCES game_groups(id) ON DELETE CASCADE,
+    player_id           UUID NOT NULL REFERENCES players(id) ON DELETE CASCADE,
+    role                VARCHAR(50) NOT NULL CHECK (role IN ('Owner', 'CoGm')),
+    added_by_player_id  UUID REFERENCES players(id) ON DELETE SET NULL,
+    created_at          TIMESTAMPTZ NOT NULL DEFAULT now(),
+    UNIQUE (group_id, player_id)
+);
+
+INSERT INTO group_managers (group_id, player_id, role)
+SELECT gg.id, p.id, 'Owner'
+FROM game_groups gg
+JOIN players p ON p.telegram_id = gg.gm_telegram_id
+ON CONFLICT (group_id, player_id) DO NOTHING;
+
+CREATE INDEX ix_group_managers_group_role ON group_managers (group_id, role);
+CREATE INDEX ix_group_managers_player ON group_managers (player_id);