docs: link Mermaid diagrams from 8 architecture/framework docs

Wire the new docs/diagrams/exported/*.svg into the documents that
already describe each flow, with the .mmd source linked alongside so
edits stay auditable:

- CLAUDE.md                       resilience-3layers
- docs/ARCHITECTURE.md            request-pipeline + resilience-3layers
- docs/AUTO-COMBO.md              auto-combo-9factor
- docs/RESILIENCE_GUIDE.md        resilience-3layers
- docs/I18N.md                    i18n-flow
- docs/MCP-SERVER.md              mcp-tools-37
- docs/CLOUD_AGENT.md             cloud-agent-flow
- docs/AUTHZ_GUIDE.md             authz-pipeline
- docs/CODEBASE_DOCUMENTATION.md  request-pipeline + db-schema-overview

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/CODEBASE_DOCUMENTATION.md

@@ -286,6 +286,10 @@ Top-level files in `src/lib/`:
 Singleton SQLite database (`getDbInstance()` in `core.ts`, WAL journaling).
 **Never write raw SQL in routes or handlers** — go through these modules.
 
+![Database schema overview (selected core tables)](./diagrams/exported/db-schema-overview.svg)
+
+> Source: [diagrams/db-schema-overview.mmd](./diagrams/db-schema-overview.mmd)
+
 Domain modules (each owns one or more tables): `apiKeys.ts`, `backup.ts`,
 `batches.ts`, `cleanup.ts`, `cliToolState.ts`, `combos.ts`,
 `commandCodeAuth.ts`, `compression.ts`, `compressionAnalytics.ts`,
@@ -638,6 +642,10 @@ Common commands:
 
 ## 9. Request Pipeline (Summary)
 
+![Request pipeline (/v1/chat/completions)](./diagrams/exported/request-pipeline.svg)
+
+> Source: [diagrams/request-pipeline.mmd](./diagrams/request-pipeline.mmd)
+
 ```
 Client request
   → /v1/chat/completions (route.ts)