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:
- The 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.

docker/promtail/config.yaml

@@ -60,11 +60,6 @@ scrape_configs:
         regex: "mana-mon-.*"
         target_label: "tier"
         replacement: "monitoring"
-      # mana-matrix-* → tier=matrix
-      - source_labels: ["container"]
-        regex: "mana-matrix-.*"
-        target_label: "tier"
-        replacement: "matrix"
       # mana-game-* → tier=games
       - source_labels: ["container"]
         regex: "mana-game-.*"