chore: clean up previous-version cruft and fix README accuracy

Remove files from the PocketBase/mock-response era and fix stale docs:

Deleted:
- RELEASE_NOTES_v1.1.0.md (PocketBase integration release)
- RELEASE_NOTES_v1.2.0.md (mock-responses 'gradual real' release)
- config.example.json (described a JSON config-file schema the app never
  read; config is env vars + CLI flags only) — also dropped from goreleaser
- MANUAL_TEST_GUIDE.md (PocketBase/mock-era manual test steps)
- FRAMEWORK_LIBRARY_PATTERNS.json (malformed JSON, unreferenced by any code)

README accuracy:
- Fixed 5 dangling links to security-pattern docs that live only on the
  docs site -> point to rainmana.github.io/tinybrain/security-patterns/
- Version badge v1.2.1 -> v3.0.1
- Replaced obsolete 'main redeclared' (v1.2.0) troubleshooting with the
  real /v3 module-path guidance, incl. the 'module path must match major
  version' error users hit on go install

Kept: CWE_LLM_DATASET.json (valid, referenced), OFFICIAL_DATA_SOURCES.md,
examples/, test_scenarios/, test_data/, and the .cursorrules/.roo-mode/
.clinerules dev-tool configs (all current, no stale markers).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: rainmana

.goreleaser.yml

@@ -46,7 +46,6 @@ archives:
     files:
       - README.md
       - LICENSE
-      - config.example.json
 
 checksum:
   name_template: 'checksums.txt'