Feat v0.2.6 admin settings audit (#10)

Roadmap reorder: Extension Lifecycle moved to v0.3.x, settings audit
milestones renumbered (v0.2.7→v0.2.6, v0.2.8→v0.2.7, v0.2.9→v0.2.8).
Added v0.2.9 for builtin extension retirement — 6 chat-centric
extensions (csv-table, diff-viewer, js-sandbox, katex, mermaid, regex)
are dormant until a chat surface ships; roadmap tracks converting them
to regular packages and removing the auto-seed mechanism.

Admin settings E2E verified — all 7 sections (default surface,
registration, banner, message bar, footer, vault, email) render and
save correctly. Packages surface verified (17/17 loaded).

Dead code removed:
- sectionCategory(): AI/routing/channel cases, default→system
- PublicSettings(): system_prompt, retention_ttl, paste_to_file,
  allow_user_personas
- PolicyDefaults: allow_raw_model_access, default_model
- Profile handlers: allow_raw_model_access, kb_direct_access lookups
- Test seeds: model_roles setting, allow_raw_model_access policy
- packages.js: 'chat' from CORE_IDS

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

server/database/testhelper.go

@@ -335,15 +335,13 @@ func TruncateAll(t *testing.T) {
 			INSERT INTO global_settings (key, value) VALUES
 				('registration', '{"enabled": true}'),
 				('site', '{"name": "Switchboard Core", "tagline": "Self-hosted extension platform"}'),
-				('banner', '{"enabled": false, "text": "", "bg": "#007a33", "fg": "#ffffff"}'),
-				('model_roles', '{"utility":{"primary":null,"fallback":null},"embedding":{"primary":null,"fallback":null},"generation":{"primary":null,"fallback":null}}')
+				('banner', '{"enabled": false, "text": "", "bg": "#007a33", "fg": "#ffffff"}')
 			ON CONFLICT (key) DO NOTHING
 		`)
 		DB.Exec(`
 			INSERT INTO platform_policies (key, value) VALUES
 				('allow_user_byok',         'false'),
 				('allow_user_personas',     'false'),
-				('allow_raw_model_access',  'true'),
 				('allow_registration',      'true'),
 				('default_user_active',     'false'),
 				('allow_team_providers',    'true')
@@ -354,19 +352,13 @@ func TruncateAll(t *testing.T) {
 			INSERT INTO global_settings (key, value) VALUES
 				('registration', '{"enabled": true}'::jsonb),
 				('site', '{"name": "Switchboard Core", "tagline": "Self-hosted extension platform"}'::jsonb),
-				('banner', '{"enabled": false, "text": "", "bg": "#007a33", "fg": "#ffffff"}'::jsonb),
-				('model_roles', '{
-					"utility":    { "primary": null, "fallback": null },
-					"embedding":  { "primary": null, "fallback": null },
-					"generation": { "primary": null, "fallback": null }
-				}'::jsonb)
+				('banner', '{"enabled": false, "text": "", "bg": "#007a33", "fg": "#ffffff"}'::jsonb)
 			ON CONFLICT (key) DO NOTHING
 		`)
 		DB.Exec(`
 			INSERT INTO platform_policies (key, value) VALUES
 				('allow_user_byok',         'false'),
 				('allow_user_personas',     'false'),
-				('allow_raw_model_access',  'true'),
 				('allow_registration',      'true'),
 				('default_user_active',     'false'),
 				('allow_team_providers',    'true')