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/static/swagger.html

@@ -4,7 +4,7 @@
   <meta charset="utf-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1" />
   <meta name="color-scheme" content="light dark" />
-  <title>Chat Switchboard — API Docs</title>
+  <title>Switchboard Core — API Docs</title>
   <link rel="stylesheet" href="https://unpkg.com/swagger-ui-dist@5/swagger-ui.css" />
   <style>
     /* ── Palette — WCAG AA 4.5:1 minimum contrast ────────────────── */