feat: add room information

[hmans]

Summary

• Add channel-only Room Information backed by a dedicated RoomInformationChangedEvent.
• Add member/manager-gated GraphQL reads and a updateRoomInformation mutation.
• Add the Room Sidebar information tab and the server-admin room detail page for details, Markdown Room Information, and permissions.
• Document the new event/projection/API surface in FDR-019, architecture inventory, and glossary.

Fixes #896

Test Plan

• mise codegen-cli
• mise codegen-frontend
• go test ./internal/core -run 'TestChattoCore_UpdateRoomInformation|TestRoomCatalogProjection|TestEventFacts' -count=1
• go test ./internal/graph -run 'TestRoom|TestMutation|TestAdmin' -count=1
• go test ./internal/graph -run 'TestRoomInformation_AccessControl|TestUpdateRoomInformation_Authorization' -count=1
• go test ./internal/core ./internal/graph -count=1
• pnpm vitest --run 'src/lib/storage/roomSidebarPanel.spec.ts' 'src/routes/chat/[serverId]/[roomId]/roomSidebarPanels.svelte.spec.ts' 'src/routes/chat/[serverId]/[roomId]/RoomSidebarToggle.svelte.spec.ts' 'src/routes/chat/[serverId]/[roomId]/RoomSidebar.svelte.spec.ts'
• pnpm check
• mise lint-frontend
• Browser verification in Chrome DevTools MCP at desktop and mobile widths for the room sidebar information tab and server-admin room detail page.