Add room support for multi-session pointing poker

[rdlucas2]

Summary

• Add normalized DB schema with rooms, room_players (junction table), and room-scoped stories tables with foreign keys
• Users must provide both a name and room ID on the home page; missing either redirects back to /
• SSE broadcasts are now scoped per-room — players only receive events from their own room
• Timer and points visibility state are per-room instead of global

Test plan

• Delete existing pointing.db before running (schema changed)
• Verify home page requires both name and room ID fields
• Join the same room from two browsers and confirm SSE events sync between them
• Join different rooms from two browsers and confirm events are isolated
• Verify duplicate names are rejected within the same room but allowed across rooms
• Test clear, show/hide, observer toggle, and timer reset work per-room

🤖 Generated with Claude Code