fix(dashboard): filter polecats by registered rigs

FetchPolecats() was showing all tmux sessions system-wide without
filtering by the workspace's registered rigs. This caused unrelated
refineries (like roxas) to appear in the dashboard.

Now loads rigs.json and only displays sessions for registered rigs,
matching the filtering behavior already used in FetchMergeQueue().

Fixes gh-868

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/web/fetcher.go

@@ -623,6 +623,19 @@ func determineColorClass(ciStatus, mergeable string) string {
 
 // FetchPolecats fetches all running polecat and refinery sessions with activity data.
 func (f *LiveConvoyFetcher) FetchPolecats() ([]PolecatRow, error) {
+	// Load registered rigs to filter sessions
+	rigsConfigPath := filepath.Join(f.townRoot, "mayor", "rigs.json")
+	rigsConfig, err := config.LoadRigsConfig(rigsConfigPath)
+	if err != nil {
+		return nil, fmt.Errorf("loading rigs config: %w", err)
+	}
+
+	// Build set of registered rig names
+	registeredRigs := make(map[string]bool)
+	for rigName := range rigsConfig.Rigs {
+		registeredRigs[rigName] = true
+	}
+
 	// Query all tmux sessions with window_activity for more accurate timing
 	cmd := exec.Command("tmux", "list-sessions", "-F", "#{session_name}|#{window_activity}")
 	var stdout bytes.Buffer
@@ -663,6 +676,11 @@ func (f *LiveConvoyFetcher) FetchPolecats() ([]PolecatRow, error) {
 		rig := nameParts[1]
 		polecat := nameParts[2]
 
+		// Skip rigs not registered in this workspace
+		if !registeredRigs[rig] {
+			continue
+		}
+
 		// Skip non-worker sessions (witness, mayor, deacon, boot)
 		// Note: refinery is included to show idle/processing status
 		if polecat == "witness" || polecat == "mayor" || polecat == "deacon" || polecat == "boot" {