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>

chart/values.yaml

@@ -1,10 +1,10 @@
-# Chat Switchboard — Helm values
+# Switchboard Core — Helm values
 # helm install switchboard ./chart
 
 # ── Images ─────────────────────────────────
 backend:
   image:
-    repository: git.gobha.me/xcaliber/chat-switchboard
+    repository: git.gobha.me/switchboard/core
     tag: ""  # defaults to Chart.appVersion
     pullPolicy: IfNotPresent
   replicaCount: 2  # v0.32.0: multi-replica HA
@@ -19,7 +19,7 @@ backend:
 
 frontend:
   image:
-    repository: git.gobha.me/xcaliber/chat-switchboard-frontend
+    repository: git.gobha.me/switchboard/core
     tag: ""  # defaults to Chart.appVersion
     pullPolicy: IfNotPresent
   replicaCount: 1