fix(store): scope SetDomainStatus by project (IDOR); scheduler reuses DeriveStatus

handleCheck's error branch wrote last_check_status via an id-only UPDATE, so
an authenticated caller's own valid project id paired with a foreign domain
id in the URL could flip a stranger's domain to "error" even though Check
itself is project-scoped and would 404/error out first. Add project_id to
the WHERE clause (queries/domains.sql + generated db/domains.sql.go), thread
projectID through Store/TenantStore/SchedStore SetDomainStatus, and pass pid
from context at both call sites in handleCheck plus the scheduler.

Also collapse checkDomain's inline status derivation in scheduler.go into a
call to service.DeriveStatus, the same helper handleCheck already uses, so
there's a single source of truth for "drift vs in_sync" instead of two
copies that could drift apart.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwxdSt4reTm7Dj1oxRvpP3

internal/store/queries/domains.sql

@@ -33,7 +33,7 @@ WHERE d.id = $1 AND d.project_id = $2;
 SELECT last_check_status FROM domains WHERE id = $1;
 
 -- name: SetDomainStatus :exec
-UPDATE domains SET last_check_status = $2 WHERE id = $1;
+UPDATE domains SET last_check_status = $2 WHERE id = $1 AND project_id = $3;
 
 -- name: CountDriftDomains :one
 SELECT count(*) FROM domains WHERE last_check_status = 'drift';