Add invite request system and Gitea Actions CI/CD pipeline

Invite request feature:
- Public form to request an invite when INVITE_REQUEST_ENABLED=true
- Stores requests in new invite_requests DB table
- Emails admins on new request, emails requester on approve/deny
- Admin panel tab to review, approve, and deny requests
- Approval auto-creates invite code and sends signup link

CI/CD pipeline:
- Build & push Docker image to Gitea registry on release
- Auto-deploy to staging with health check
- Manual workflow_dispatch for production deploys

Also includes client layout/sizing improvements for card grid
and opponent spacing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/stores/user_store.py

@@ -133,6 +133,20 @@ CREATE TABLE IF NOT EXISTS invite_codes (
     is_active BOOLEAN DEFAULT TRUE
 );
 
+-- Invite requests table
+CREATE TABLE IF NOT EXISTS invite_requests (
+    id BIGSERIAL PRIMARY KEY,
+    name VARCHAR(100) NOT NULL,
+    email VARCHAR(255) NOT NULL,
+    message TEXT,
+    status VARCHAR(20) DEFAULT 'pending',
+    ip_address INET,
+    created_at TIMESTAMPTZ DEFAULT NOW(),
+    reviewed_at TIMESTAMPTZ,
+    reviewed_by UUID REFERENCES users_v2(id),
+    invite_code_id BIGINT REFERENCES invite_codes(id)
+);
+
 -- Player stats table (extended for V2 leaderboards)
 CREATE TABLE IF NOT EXISTS player_stats (
     id BIGSERIAL PRIMARY KEY,