refactor: eliminate string/magic-number literals (goconst, mnd) and fix const-type grouping (SA9004)

- upload/task: taskCategoryUpload/taskQueueDefault 常量替代 8 处字面量
- admin: 复用既有 logDBNameSQLite 常量替代 3 处 "sqlite" 字面量
- pkg/cache/disk: defaultCleanupInterval 命名常量
- driver_asynq_worker/executor: 分离 contextKey 类型常量组
lint_issues 45→34, tests 44/44

.auto/log.jsonl

@@ -1 +1,2 @@
 {"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"}}