fix: rebase onto main, fix SQLite concurrency, lint clean

- Add busy_timeout PRAGMA and MaxOpenConns(1) for SQLite stability
- Use per-test temp DB in handler tests to prevent state leaks
- Pre-allocate migrations slice (prealloc lint)
- Remove invalid linter names (wsl_v5, noinlineerr) from .golangci.yml
- Remove unused //nolint:gosec directives
- Replace context.Background() with t.Context() in tests
- Use goimports formatting for all files
- All make check passes with zero failures

.golangci.yml

@@ -11,10 +11,8 @@ linters:
     - depguard
     - godot
     - wsl
-    - wsl_v5
     - wrapcheck
     - varnamelen
-    - noinlineerr
     - dupl
     - paralleltest
     - nlreturn