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>

categories.md

@@ -0,0 +1,26 @@
+# Expense Categories
+
+Pick exactly one per entry. Default to `Other` rather than invent a new category.
+
+- Food & Drink
+- Groceries
+- Transport
+- Travel & Lodging
+- Entertainment
+- Shopping
+- Health & Medical
+- Utilities
+- Housing & Rent
+- Fees & Services
+- Gifts & Donations
+- Work & Office
+- Education
+- Other
+
+## Picking tips
+- **Food & Drink** = restaurants, cafes, takeaway, bars.
+- **Groceries** = supermarkets, wet markets, bulk food stores (even if also selling prepared food).
+- **Transport** = taxi, MTR, bus, fuel, parking, tolls.
+- **Travel & Lodging** = hotels, flights, trains (intercity), Airbnb.
+- **Fees & Services** = bank charges, subscriptions, laundry, repairs.
+- **Work & Office** = supplies, co-working, work-related software.