docs(readme): drop .xlsx from known gaps (covered in 2h)

README.md

@@ -128,14 +128,15 @@ that a green scan means safe content:
   inbox showcase (`tests/test_okf_inbox_uploads.py` + `tests/inbox_frontend.py`, a
   dev-scoped demonstration whose `python-docx`/`python-pptx` parsers live in the
   `[dev]` extra, never core `dependencies`) reads `.txt`/`.md`/`.csv`/`.docx`/
-  `.pptx`, folders and `.zip`, materializes them into an OKF bundle, then guards
-  it. What survives text extraction is **out of scope**: VBA/macros
+  `.pptx`/`.xlsx`, folders and `.zip`, materializes them into an OKF bundle, then
+  guards it. What survives text extraction is **out of scope**: VBA/macros
   (`.docm`/`.xlsm`/`.pptm`), OLE / embedded objects, image-embedded instructions
   needing OCR, font/render steganography, and encrypted / password-protected files
   — the binary layer needs a separate scanner. The front-end owns the container
   threats it *can* see (zip-slip → path gate, zip-bomb → size cap, symlink
-  refusal, CSV formula-lead cells). Known gaps: `.xlsx` (openpyxl) and `.pdf`
-  extraction, and the numeric `-`/`+` CSV false positive.
+  refusal, CSV/XLSX formula-lead cells). Known gaps: `.pdf` extraction, and the
+  numeric `-`/`+` CSV false positive (an XLSX numeric cell is typed, so it does not
+  trip the gate).
 - **Lexicon findings are deduplicated by pattern id** — `count=1` and the first
   offset are reported, so the same class matched across several channels/variants
   collapses to one finding at its first location. This keeps reports readable, but