chore(bf-a8031): remove tracked debug/scratch artifacts and compiled binaries

Remove 7 tracked files from repo root:
- --1.ppm (scratch PPM image)
- 0 (scratch output)
- gen_fixtures (compiled binary)
- mod (compiled binary)
- out.pdf (scratch PDF)
- test_trailer_parse (compiled test binary)
- test_trailer_parse2 (compiled test binary)

.gitignore already contains patterns to prevent re-tracking these files.
Test fixtures in tests/fixtures/ remain intact.

Verification: notes/bf-a8031.md

Closes bf-a8031

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notes/bf-a8031.md

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+# bf-a8031 - Repo-root hygiene cleanup
+
+## Summary
+Removed tracked debug/scratch artifacts and compiled binaries from git repository root.
+
+## Files removed (7 total)
+- `--1.ppm` - Scratch PPM image output file
+- `0` - Scratch output file (malformed name)
+- `gen_fixtures` - Compiled binary (fixture generator)
+- `mod` - Compiled binary
+- `out.pdf` - Scratch PDF output
+- `test_trailer_parse` - Compiled test binary
+- `test_trailer_parse2` - Compiled test binary
+
+## Verification
+### PASS
+- All 7 files were tracked in git and have been staged for removal
+- `.gitignore` already contains patterns to prevent re-tracking:
+  - `0` and `--1.ppm` explicitly listed
+  - `gen_fixtures` explicitly listed  
+  - `mod` explicitly listed
+  - `out.pdf` explicitly listed
+  - `test_trailer_parse*` covered by `test_*` pattern
+  - `*.rlib`, `*.bak` patterns for compiled libraries and backups
+- No other tracked compiled binaries or scratch artifacts found in root
+- No tracked .rlib, .a, .o, .so, .dylib, .exe, or .dll files
+- Test fixtures in `tests/fixtures/` remain intact (legitimate test data)
+
+### Notes
+- Python scripts in repo root (assess_doc_coverage.py, audit_docs.py, etc.) are legitimate development utilities, not scratch artifacts
+- Debug/test example files in `crates/*/examples/` and `crates/*/tests/` are in proper locations and should remain
+- No `serve.rs.bak` file was found (already cleaned up)
+
+## Commit
+Single commit removing all 7 tracked artifacts: `chore(bf-a8031): remove tracked debug/scratch artifacts and compiled binaries`