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>

CHANGELOG.md

@@ -2,6 +2,32 @@
 
 All notable changes to Switchboard Core are documented here.
 
+## [Unreleased] — v0.2.6
+
+### Changed
+
+- **Roadmap reorder**: Extension Lifecycle moved from v0.2.6 to v0.3.x
+  (Workflows series). 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 (chat-centric extensions dormant until chat surface ships).
+
+### Removed
+
+- **Dead admin section categories** in `sectionCategory()`: AI (providers,
+  models, personas, roles, knowledgeBases, memory), routing (health, routing,
+  capabilities), and channels. Default category changed from `ai` to `system`.
+- **Dead PublicSettings fields**: `system_prompt`/`has_admin_prompt`,
+  `retention_ttl_days`, `paste_to_file_chars`, `allow_user_personas` policy
+  — all chat-era with no frontend consumers.
+- **Dead PolicyDefaults**: `allow_raw_model_access`, `default_model`.
+- **Dead policy lookups**: `allow_raw_model_access` and `kb_direct_access`
+  from profile bootstrap and permissions handlers.
+- **Dead test seed data**: `model_roles` global setting, `allow_raw_model_access`
+  policy from test helper.
+- **Dead CORE_IDS entry**: Removed `chat` from packages admin page.
+
+---
+
 ## [Unreleased] — v0.2.5
 
 ### Added