fix category missing codes after merge

[MythodeaLoL]

Fix: Accurate category detection for watch/import; enforce Default category; API key override; UI and config updates

Description

This PR fixes category detection regressions introduced after merging commit 2e9d7dd into 4248c3d and brings parity with the changes from branch 04.01.26-drondeseries-altmount-main.

Summary of changes

• Fix watcher category detection: the watcher no longer uses the first path segment as a category. Category is detected only when the watched file path starts with a configured SABnzbd category subdirectory (longest-prefix match).
• Ensure imported files under /import are recognized as category imports when placed inside a configured category path.
• Upload via UI (/queue) with a selected category correctly resolves to that category's directory (behavior verified).
• Add a system Default category:
  • Name is immutable ("Default"), cannot be removed or renamed via UI.
  • Default is configurable in YAML with order, priority, and dir (dir defaults to complete, no leading slash).
  • Default category values are loaded/saved from config.yaml (no hardcoded path).
• Make sabnzbd.complete_dir a virtual path relative to the mount point (default /) and normalize dirs without leading slashes.
• Add API key override in config.yaml:
  • config.api.key_override (32 chars) is used instead of the DB key if set and valid.
  • Regenerating the API key will also update key_override when present.
• UI changes:
  • Category inputs replaced by selects (None + existing SABnzbd categories) in Upload NZB Files and ARR config pages.
  • Default category UI: name readonly, but order/priority/dir editable.
• Misc fixes:
  • Replaced usage of a non-existing ConfigManager method with UpdateConfig + SaveConfig.
  • Logging improved to show category values instead of pointer addresses.
• Tests: added/updated tests for category detection and related handlers.

Key files changed

• Backend:
  • internal/importer/scanner/watcher.go (getCategoryFromPath, watcher logic)
  • internal/importer/service.go (buildCategoryPath / calculateProcessVirtualDir)
  • internal/config/manager.go (Default category enforcement, complete_dir handling, API key override)
  • internal/api/parsers.go (validateAPIKey)
  • internal/api/auth_handlers.go (regenerate API key / config save)
  • internal/api/sabnzbd_handlers.go (getDefaultCategory / buildCategoryPath)
  • config.sample.yaml
• Frontend:
  • frontend/src/components/config/SABnzbdConfigSection.tsx (Default category UI)
  • frontend/src/components/config/ArrsConfigSection.tsx (category select)
  • frontend/src/components/config/ArrsInstanceCard.tsx (category select prop)
  • frontend/src/components/queue/DragDropUpload.tsx (category select)
• Misc: logging and handler fixes

Migration / Upgrade notes

• Update config.yaml to include the Default category and optionally api.key_override (see config.sample.yaml).
• sabnzbd.complete_dir is now relative to the mount point; remove leading slashes in dir values (code normalizes them but keep this in mind).
• Confirm Default category values in your config if you previously relied on implicit/hardcoded defaults.

How to test

1. Configure SABnzbd categories (e.g., sonarr/, filmes/download/mov).
2. Place an NZB in the watch dir under a category path:
   • e.g. /.../sync_nzbs/filmes/download/mov/torrent/interestelar.nzb
   • Confirm the matching category is applied and the import ends in the category dir.
3. Import files manually into /import inside a category path and confirm category detection.
4. Upload via Upload NZB Files (/queue) and select a category — confirm file goes to category dir.
5. Confirm Default category exists in UI and cannot be renamed/removed; verify order/priority/dir editable.
6. Set config.api.key_override to a 32-char key and verify API auth uses it. Regenerate the API key in UI and confirm both DB and config are updated.