feat: let Tidy rules match files by type

[AmrMsCLL]

Stacked on #46. This is 11d of as2026-10-05-strata-phase-11-next-batch-2.md.

What changes

• A Tidy tagging rule can match a file type: images, PDFs, documents, spreadsheets, presentations, zip archives or text files. These are the types uploads accept.
• "Title contains" is optional once a type is chosen. A rule needs words, a type, or both.
• Types come from the stored MIME type, which uploads already check against the file's content. The Office MIME types are now exported from file-inspection.ts, so Tidy uses the same list.
• Rule lists, the delete dialog and Tidy history describe file-type rules ("PDFs → Finance").

Migration

20261005100000_tidy_file_types:

ALTER TABLE "tidy_rules" ADD COLUMN "file_type" TEXT;
ALTER TABLE "tidy_rules" ALTER COLUMN "title_contains" SET DEFAULT '';

Contract

• Tidy rules gain fileType. POST /spaces/:id/tidy-rules accepts fileType, and titleContains is now optional. Tidy history's rule gains fileType.

Verification

• Server: test/integration/tidy.spec.ts (6 passed) and test/file-inspection.spec.ts (4 passed).
• Frontend: test/tidy.spec.tsx (5 passed).
• Lint and build pass.