AUR-574: generic text files are reviewed, never dropped by a documentation grammar

Measurement (before the fix)

Ran the real binary (review --base HEAD~1) over tests/fixtures/repos/git-demo with AURUMCODE_PROMPT_CAPTURE, inside the shared Go container. The runtime detects NOTES.txt and config/demo-tokens.txt as grammar vimdoc (chosen only because of the generic .txt extension) and the catalog files vimdoc under documentation. Captured prompt:

- vimdoc: 2 files
## Code Changes

## Review Coverage
- Code files in this diff: 0
- Code files fully reviewed (every hunk included): 0
- Documentation files excluded from the code rule catalog (...): 2
  - NOTES.txt
  - config/demo-tokens.txt

The model never saw the hard-coded token that only the deterministic pass reports: a confidently wrong answer.

Acceptance timing

tests/acceptance/AUR-574.sh all (git-demo prompt, e2e AUR-441 with the binary built once, unit tests, tutorial check, MUT-001) measured 73 s in the shared container. Running AUR-541.sh all inside it took 9m37s in total, over the 600 s sealed budget, so it is the separate selector AC-001-full, run by the validation step. AUR-541.sh all passed unedited in that earlier full run.