fix: resolve all linting and formatting issues

- Fix error return value checks (errcheck)
- Fix unused parameters by using underscore prefix
- Add missing package comments to all packages
- Fix context key type issue in middleware (use typed contextKey)
- Replace deprecated trace.NewNoopTracerProvider with noop.NewTracerProvider
- Fix embedded field selector in database client
- Remove trailing whitespace
- Remove revive linter (as requested) to avoid stuttering warnings for public API interfaces

All linting and formatting checks now pass.

AGENTS.md

@@ -184,6 +184,7 @@ When working on this project, follow this workflow:
 - Meet the acceptance criteria
 - Use the implementation notes as guidance
 - Follow the patterns established in `playbook.md`
+- Implement tests
 
 ### 6. Verify Alignment
 - Ensure code follows Clean/Hexagonal Architecture principles
@@ -196,6 +197,8 @@ When working on this project, follow this workflow:
 - **ALWAYS commit** after successful implementation
 - Ensure the code builds (`go build`)
 - Ensure all tests pass (`go test`)
+- Ensure there are no linter issues (`make lint`)
+- Ensure there are no fmt issues (`make fmt-check`)
 - Verify all acceptance criteria are met
 - Write a clear, descriptive commit message
 
@@ -301,6 +304,7 @@ If you make architectural decisions or significant changes:
 2. Update architecture documents if structure changes
 3. Update stories if implementation details change
 4. Keep documentation in sync with code
+5. Do not use any emojis
 
 ---