Phase 6 — The console, properly

The console grows from "enough to enter four campaigns" into the administrative surface it was always meant to be: agenda and month views, campaign pages, and per-campaign ICS feeds served from D1. Discord login and role gating already exist from phase 2. The design system in `design/` is the reference.

## In order
1. #43 — Agenda, month view, session detail
1. #44 — Campaign and game-day pages; games, settings, audit log
1. #45 — Per-campaign ICS feeds from D1 with feed_token

Read the design/ system and then the three linked issues: #43 for agenda, month view, and session detail; #44 for campaign and game-day pages; and #45 for per-campaign ICS feeds from D1. Done means all listed console surfaces and feed behavior are implemented while using the existing Discord login and role gating.

索引モデルが issue の本文から書いたものです。