Initial commit: bookkeeping skill

Receipt-image to Google Sheets expense logger with HKD conversion.
Includes SKILL.md, categories/schema reference, config template,
and Python scripts for FX conversion (frankfurter.app) and Sheets append.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

config.example.json

@@ -0,0 +1,6 @@
+{
+  "sheet_id": "PUT_GOOGLE_SHEET_ID_HERE",
+  "worksheet": "Expenses",
+  "service_account_path": "~/.config/gcp/bookkeeping-sa.json",
+  "hkd_fx_provider": "frankfurter"
+}