feat(v1.1.8): F3 realtime auth_mode = 'session' (migration 0033)

Migration 0033 widens topics.auth_mode CHECK to include 'session'
alongside 'public' and 'token'.

TopicAuthMode enum gains a Session variant (as_str + from_db
extended uniformly).

RealtimeAuthorityImpl now takes Arc<dyn UsersService> as a third
constructor arg. The Session branch of authorize_subscribe
delegates to UsersService::verify_session_for_realtime(app_id,
token):
  * Returns Some(user) → allow. The service bumps the sliding TTL
    on success.
  * Returns None → Unauthorized.
  * Defense-in-depth: even though verify_session_for_realtime
    already enforces cross-app isolation, the branch re-checks
    user.app_id == app_id.

Tests added (4 new cases): valid session token allows; missing
token is Unauthorized; wrong token is Unauthorized; cross-app
session token is Unauthorized. All 12 realtime_authority tests
pass.

Dashboard: TopicAuthMode TypeScript union widened to include
'session'; the topic create + edit forms gain a third radio option
labeled "session — requires a per-app user session minted by
users::login (v1.1.8)".

picloud binary: construction order reshuffled so users is built
before realtime_authority. app_secrets_repo is now .clone()'d into
the pubsub realtime wiring so the original Arc can be re-used by
realtime_authority.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/migrations/0033_topics_auth_mode_session.sql

@@ -0,0 +1,14 @@
+-- v1.1.8 F3 — extend topics.auth_mode CHECK to allow 'session'.
+--
+-- v1.1.6 shipped 'public' + 'token'. v1.1.8 adds 'session' so a
+-- topic can authorize SSE subscribers against a per-app user session
+-- minted by users::login. The realtime authority delegates verify to
+-- UsersService::verify_session_for_realtime, which returns the user
+-- on success; the subscription proceeds with that principal.
+--
+-- 'script' (v1.2 script-mediated subscribe auth) extends the
+-- constraint a third time later.
+
+ALTER TABLE topics DROP CONSTRAINT IF EXISTS topics_auth_mode_check;
+ALTER TABLE topics ADD CONSTRAINT topics_auth_mode_check
+    CHECK (auth_mode IN ('public', 'token', 'session'));