fix(mana-auth) + chore: rewrite /api/v1/auth/login JWT mint, remove Matrix stack

This commit bundles two unrelated changes that were swept together by an
accidental `git add -A` in another working session. Documented here so the
history reflects what's actually inside.

═══════════════════════════════════════════════════════════════════════
1. fix(mana-auth): /api/v1/auth/login mints JWT via auth.handler instead
   of api.signInEmail
═══════════════════════════════════════════════════════════════════════

Previous attempt (commit 55cc75e7d) tried to fix the broken JWT mint in
/api/v1/auth/login by switching the cookie name from `mana.session_token`
to `__Secure-mana.session_token` for production. That was necessary but
not sufficient: Better Auth's session cookie value isn't just the raw
session token, it's `<token>.<HMAC>` where the HMAC is derived from the
better-auth secret. Reconstructing the cookie from auth.api.signInEmail's
JSON response only gave us the raw token, so /api/auth/token's
get-session middleware still couldn't validate it and the JWT mint kept
silently failing.

Real fix: do the sign-in via auth.handler (the HTTP path) rather than
auth.api.signInEmail (the SDK path). The handler returns a real fetch
Response with a Set-Cookie header containing the fully signed cookie
envelope. We capture that header verbatim and forward it as the cookie
on the /api/auth/token request, which now passes validation and mints
the JWT correctly.

Verified end-to-end on auth.mana.how:

  $ curl -X POST https://auth.mana.how/api/v1/auth/login \
      -d '{"email":"...","password":"..."}'
  {
    "user": {...},
    "token": "<session token>",
    "accessToken": "eyJhbGciOiJFZERTQSI...",   ← real JWT now
    "refreshToken": "<session token>"
  }

Side benefits:
- Email-not-verified path is now handled by checking
  signInResponse.status === 403 directly, no more catching APIError
  with the comment-noted async-stream footgun.
- X-Forwarded-For is forwarded explicitly so Better Auth's rate limiter
  and our security log see the real client IP.
- The leftover catch block now only handles unexpected exceptions
  (network errors etc); the FORBIDDEN-checking logic in it is dead but
  harmless and left in for defense in depth.

═══════════════════════════════════════════════════════════════════════
2. chore: remove the entire self-hosted Matrix stack (Synapse, Element,
   Manalink, mana-matrix-bot)
═══════════════════════════════════════════════════════════════════════

The Matrix subsystem ran parallel to the main Mana product without any
load-bearing integration: the unified web app never imported matrix-js-sdk,
the chat module uses mana-sync (local-first), and mana-matrix-bot's
plugins duplicated features the unified app already ships natively.
Keeping it alive cost a Synapse + Element + matrix-web + bot container
quartet, three Cloudflare routes, an OIDC provider plugin in mana-auth,
and a steady drip of devlog/dependency churn.

Removed:
- apps/matrix (Manalink web + mobile, ~150 files)
- services/mana-matrix-bot (Go bot with ~20 plugins)
- docker/matrix configs (Synapse + Element)
- synapse/element-web/matrix-web/mana-matrix-bot services in
  docker-compose.macmini.yml
- matrix.mana.how/element.mana.how/link.mana.how Cloudflare tunnel routes
- OIDC provider plugin + matrix-synapse trustedClient + matrixUserLinks
  table from mana-auth (oauth_* schema definitions also removed)
- MatrixService import path in mana-media (importFromMatrix endpoint)
- Matrix notification channel in mana-notify (worker, metrics, config,
  channel_type enum, MatrixOptions handler)
- Matrix entries from shared-branding (mana-apps + app-icons),
  notify-client, the i18n bundle, the observatory map, the credits
  app-label list, the landing footer/apps page, the prometheus + alerts
  + promtail tier mappings, and the matrix-related deploy paths in
  cd-macmini.yml + ci.yml

Devlog/manascore/blueprint entries that mention Matrix are left intact
as historical record. The oauth_* + matrix_user_links Postgres tables
stay on existing prod databases — code can no longer write to them, drop
them in a follow-up migration if you want them gone for real.

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

package.json

@@ -76,9 +76,6 @@
 		"dev:calendar:landing": "pnpm --filter @calendar/landing dev",
 		"dev:calendar:app": "concurrently -n api,web -c yellow,cyan \"pnpm dev:api\" \"pnpm dev:calendar:web\"",
 		"dev:calendar:full": "concurrently -n auth,sync,api -c blue,magenta,yellow \"pnpm dev:auth\" \"pnpm dev:sync\" \"pnpm dev:api\"",
-		"matrix:dev": "turbo run dev --filter=matrix...",
-		"dev:matrix:web": "pnpm --filter @matrix/web dev",
-		"dev:matrix:mobile": "pnpm --filter @matrix/mobile dev",
 		"mail:dev": "turbo run dev --filter=mail...",
 		"dev:mail:mobile": "pnpm --filter @mail/mobile dev",
 		"dev:mail:web": "pnpm --filter @mail/web dev",
@@ -230,9 +227,6 @@
 		"dev:skilltree:web": "pnpm --filter @skilltree/web dev",
 		"dev:skilltree:app": "pnpm dev:skilltree:web",
 		"dev:skilltree:full": "concurrently -n auth,sync,web -c blue,magenta,cyan \"pnpm dev:auth\" \"pnpm dev:sync\" \"pnpm dev:skilltree:web\"",
-		"dev:matrix": "cd services/mana-matrix-bot && go run ./cmd/server",
-		"build:matrix": "cd services/mana-matrix-bot && go build -ldflags=\"-s -w\" -o dist/mana-matrix-bot ./cmd/server",
-		"test:matrix": "cd services/mana-matrix-bot && go test ./...",
 		"dev:llm-playground": "pnpm --filter @mana-llm/playground dev",
 		"build:llm-playground": "pnpm --filter @mana-llm/playground build",
 		"prepare": "husky",
@@ -300,8 +294,7 @@
 		"patchedDependencies": {},
 		"overrides": {
 			"cpu-features": "npm:empty-npm-package@1.0.0",
-			"ssh2": "npm:empty-npm-package@1.0.0",
-			"@matrix-org/matrix-sdk-crypto-nodejs": "npm:empty-npm-package@1.0.0"
+			"ssh2": "npm:empty-npm-package@1.0.0"
 		}
 	}
 }