feat(ownership): import IDX above-1% XLSX holder register

Since June 2026 IDX publishes the monthly "Pemegang Saham di Atas 1%"
list as an XLSX workbook on the Data Kepemilikan Saham page instead of
a PDF announcement. Add a parser for it and accept `.xlsx` in
`ownership import --file`.

- src/ownership/xlsx.rs: zip + quick-xml reader (shared strings incl.
  rich text, sheet cells), exact 12-column header match so the daily
  above-5% and investor-type/classification workbooks are rejected,
  Excel serial dates, numeric shares, percent -> bps with float-noise
  rounding. Builds KseiHoldingDraft directly and reuses the entity
  normalizers, so investor types stay uppercase like the PDF path.
- Fixtures: trimmed excerpts of the real 2026-08-31 above-1% and
  2026-09-23 above-5% workbooks.
- Unit + CLI tests: import, ticker, releases, above-5% rejection.
- Docs: ARCHITECTURE parser pipeline, AGENTS ownership inputs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017a5Cv5Z1NzdYKgKnTiAF4E

docs/ARCHITECTURE.md

@@ -63,12 +63,16 @@ Unlike the `stocks` module (live-fetch), ownership is **import-then-query**:
 4. Fully offline after import/sync
 
 ### Data Sources
-- **KSEI** — official ≥1% shareholder registry (monthly PDF from IDX)
+- **KSEI** — official ≥1% shareholder registry, published monthly by IDX. Through May 2026 it was a PDF announcement; from the 2026-05-29 report onward it is an XLSX workbook on the IDX "Data Kepemilikan Saham" page
 - **KSEI archive** — monthly ZIP/TXT balance-position matrix, used as a local fallback/backstop import path
 - **Bing Finance** — global institutional ownership (REST API, quarterly)
 
 ### Parser Pipeline
 ```
+KSEI XLSX → zip + quick-xml (sharedStrings + sheet1) → exact 12-column header check
+  → KseiHoldingDraft (Excel serial dates, numeric shares, percent → bps)
+  → SQLite INSERT (within transaction)
+
 KSEI PDF → mutool stext (XML with coordinates) → quick-xml parse → KseiRawRow
   → normalize (ID locale numbers, dates, entity names) → KseiHolding
   → SQLite INSERT (within transaction)