fix(guide): make dev tier BCOS_ADMIN-only; keep Testing for MSP (#18)

The 'dev' audience tier was gated via isInternal() (MSP_ADMIN || BCOS_ADMIN),
so MSP admins could read developer/architecture content: technical.* and
platform.* Overviews, agent-module internals, dev Internal/Overview tabs.

Remap 'dev' to isBcos() (BCOS_ADMIN only) in visible(). Retag the 66 Testing
docs from 'audience: dev' to 'audience: internal' so MSP keeps them, per
Johannes.

Result: MSP sees Customer + Internal + Testing (66 modules); loses all
Architect/Claude/architecture. BCOS unchanged. Update platform.guide-access
to the new model.

Closes #18

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/main/resources/content/recon/recon-rules/testing.md

@@ -3,7 +3,7 @@ module: recon.recon-rules
 title: Recon Rules
 tab: Testing
 order: 35
-audience: dev
+audience: internal
 ---
 
 Frontend test checklist for **Recon Rules** (`recon.bcos.dev`). Click through in the UI and mark each row Pass or Fail.