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.

.golangci.yml

@@ -13,21 +13,11 @@ linters:
     - errcheck
     - govet
     - staticcheck
-    - revive
     - gosec
   disable:
     - gocritic  # Can be enabled later for stricter checks
 
 linters-settings:
-  revive:
-    rules:
-      - name: exported
-        severity: warning
-        arguments:
-          - checkPrivateReceivers
-          # Disable stuttering check - interface names like ConfigProvider are acceptable
-      - name: package-comments
-        severity: warning
   gosec:
     severity: medium
   errcheck:
@@ -43,10 +33,6 @@ issues:
       linters:
         - errcheck
         - gosec
-    # ConfigProvider stuttering is acceptable - it's a common pattern for interfaces
-    - path: pkg/config/config\.go
-      linters:
-        - revive
 
 output:
   print-issued-lines: true