refactor: revive cleanup — unused params to _, add missing doc comments

- admin/db_helper GetCache/GetUserService/GetAuthService: ctx -> _ (签名对称保留)
- validateMergedStorageConfig / ParseMigrationTargetConfig / MockStorageService.Put 未用参数 -> _
- SetDBServiceForTest、StorageDriver 常量组补充文档注释
lint_issues 33→26

.auto/log.jsonl

@@ -1,2 +1,3 @@
 {"ts":"2026-08-28T00:00:00Z","iter":0,"type":"baseline","metrics":{"lint_issues":45,"dup_issues":15,"tests_passed":44},"description":"baseline: 45 golangci issues (15 dupl), all tests pass","asi":{"note":"quick wins queue: gofumpt(4)+revive(8); then goconst/mnd; gosec; nilerr bug; contextcheck; dupl batches; nestif"}}
 {"ts":"2026-08-28","iter":1,"type":"keep","metrics":{"lint_issues":34,"dup_issues":15,"tests_passed":44},"delta":-11,"description":"goconst(9): taskCategoryUpload/taskQueueDefault consts in upload/task; reuse logDBNameSQLite in admin; mnd(1): defaultCleanupInterval in disk cache; staticcheck SA9004: split typed const group in asynq executor","asi":{"lesson":"golangci v2 defaults cap reporting at 50/3 - uncapped via issues:max-issues-per-linter/max-same-issues=0 (strict-only change); formatter war resolved: make format now = golangci-lint fmt (same gate as code-check), 203-file gofumpt normalization committed as infra"}}
+{"ts":"2026-08-28","iter":2,"type":"keep","metrics":{"lint_issues":33,"dup_issues":15,"tests_passed":44},"delta":-1,"description":"nilerr real bug: FlushTaskExecutionLog swallowed cache faults (non-miss errors) and silently dropped buffered task logs; now propagates wrapped error, ErrCacheMiss stays a no-op. 3 regression tests (fault / miss / persist+clear) with miniredis + stubDBService(in-memory sqlite)","asi":{"lesson":"FlushTaskExecutionLog callers in executor.go only log errors, so returning wrapped err is safe; tests need SetDBService injection since testhelper.SetupTestEnvironment targets infra/database global not admin dbService"}}