rebrand + purge orphaned frontend: Chat Switchboard → Switchboard Core

Branding: bulk rename across 50+ files (Go, JS, CSS, HTML, YAML, JSON,
shell scripts). Fix Helm chart description and git repo URLs.
Fix test helper taglines.

Admin surface: strip 14 gutted tabs (providers, models, personas,
roles, knowledge, memory, tasks, health, routing, capabilities,
channels, dashboard, usage, stats). Collapse to 4 categories:
People, Workflows, System, Monitoring.

Settings surface: strip 11 gutted tabs (models, personas, providers,
roles, knowledge, memory, usage, workflows, tasks, data, gitkeys).
Keep: general, appearance, profile, teams, connections, notifications.

Team-admin surface: strip 5 gutted tabs (personas, providers,
knowledge, tasks, usage). Keep: members, groups, connections,
workflows, settings, activity.

Components: delete chat-pane/ (13 files, 1938 lines) and
notes-pane/ (10 files, 2381 lines).

main.go: remove stale Health.Prune maintenance goroutine.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/pages/pages.go

@@ -840,7 +840,7 @@ func (e *Engine) loadFooter() FooterConfig {
 
 // loadBranding reads instance branding from global settings.
 func (e *Engine) loadBranding() (name, logoURL, tagline string) {
-	name = "Chat Switchboard" // default
+	name = "Switchboard Core" // default
 	if e.stores.GlobalConfig == nil {
 		return
 	}