R-35 (D4): dashboard sign-ins survive the controller's own restart; disk holds only a fingerprint

Sessions are keyed by sha256(cookie) and persisted to dashboard-sessions.json
(0600, tmp+fsync+rename) in the data dir: fingerprint, expiry, CSRF token.
Loaded in NewServer; expired rows dropped at load and save. Logout and
invalidateAllSessions (password change, claim reset) write the file at once.
Corrupt/unreadable file = start with no sessions (never fatal).

Red-proof: with load/save as no-ops the restart test fails ('the old cookie
no longer signs in'); with the raw token as the key the file test fails
('the sessions file holds the cookie value').

Also: TestR650_NoBareDockerExec skips a non-.go file that vanished mid-walk
(a parallel stacks test's update-journal.json.tmp raced it in a full run).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/web/server.go

@@ -282,6 +282,7 @@ func NewServer(cfg *config.Config, stackMgr *stacks.Manager, cpuCollector *syste
 	}
 
 	s.loadTemplates()
+	s.loadSessions() // R-35: dashboard sign-ins survive the controller's own restart (session_store.go)
 	go s.cleanupSessions()
 	// .fab download staging (v0.124.0): sweep aged bundles left by a crash/abandoned download.
 	if cfg.Paths.DataDir != "" {