feat(messaging): add native Matrix adapter with E2EE support

[ProductOfAmerica]

Add a full Matrix messaging adapter with end-to-end encryption, streaming responses, and frontend UI support.

Backend (src/messaging/matrix.rs)

• Password login, access token restore, and persistent session via session.json
• E2EE out of the box via matrix-sdk's e2e-encryption + sqlite store
• Streaming responses via message edits (300ms throttle)
• Typing indicators with auto-repeat
• Auto-join on room invite
• File attachment support (images, documents, audio, video via mxc:// URLs)
• DM access control (dm_allowed_users allowlist)
• History backfill for conversation context
• Message splitting at 4096-char Matrix limit

Config (src/config.rs)

• MatrixConfig and MatrixPermissions structs with hot-reload support
• Binding matching via matrix_room_id metadata key

API (src/api/server.rs)

• Matrix status in /api/messaging/status endpoint
• create_binding support with Matrix credentials
• Fix: add missing telegram field to MessagingStatusResponse

Frontend (interface/)

• Matrix platform card, setup dialog (homeserver URL, user ID, password/access token)
• Matrix binding support with optional Room ID filter
• API types for Matrix credentials and status

Docs

• matrix-setup.mdx setup guide covering account creation, TOML config, E2EE, DM access control, and platform notes

Tested:

• Password login to matrix.org
• E2EE message receive/send in encrypted rooms
• Streaming response edits
• History backfill
• Auto-join
• Frontend settings UI renders Matrix card and setup dialog
• Bindings section shows Matrix with Room ID field

[ProductOfAmerica]

@jamiepine Hey! Couple of questions:

1. matrix-sdk version — I built this against matrix-sdk 0.9 since it's the latest version compatible with sqlx 0.8. The latest matrix-sdk is 0.16, but it pulls in rusqlite 0.37 → libsqlite3-sys 0.35, which conflicts with sqlx's libsqlite3-sys 0.28-0.30 (Cargo enforces a single links = "sqlite3" in the dep graph). Upgrading to matrix-sdk 0.16 would require bumping sqlx to 0.9 (currently alpha). Any preference on how to handle this?

2. Telegram status bug — While working on this I noticed MessagingStatusResponse in server.rs was missing the telegram field entirely, so the status endpoint never reported Telegram. I included the fix in this PR since it was a one-liner — let me know if you'd prefer it as a separate commit/PR.