feat: Add equity account support to transaction filtering and Beancount import

Improvements to equity account handling across the Castle extension:

  Transaction Categorization (views_api.py):
  - Prioritize equity accounts when enriching transaction entries
  - Use two-pass lookup: first search for equity accounts, then fall back to liability/asset accounts
  - Ensures transactions with Equity:User-<id> accounts are correctly categorized as equity

UI Enhancements (index.html, index.js):
  - Add 'Equity' filter option to Recent Transactions table
  - Display blue "Equity" badge for equity entries (before receivable/payable badges)
  - Add isEquity() helper function to identify equity account entries

Beancount Import (import_beancount.py):
  - Support importing Beancount Equity:<name> accounts
  - Map Beancount "Equity:Pat" to Castle "Equity:User-<id>" accounts
  - Update extract_user_from_user_account() to handle Equity: prefix
  - Improve error messages to include equity account examples
  - Add equity account lookup in get_account_id() with helpful error if equity not enabled

These changes ensure equity accounts (representing user capital contributions) are properly distinguished from payables and receivables throughout the system.

views_api.py

@@ -318,18 +318,33 @@ async def api_get_user_entries(
     enriched_entries = []
     for entry in entries:
         # Find user_id from entry lines (look for user-specific accounts)
+        # Prioritize equity accounts, then liability/asset accounts
         entry_user_id = None
         entry_username = None
         entry_account_type = None
 
+        equity_account = None
+        other_user_account = None
+
+        # First pass: look for equity and other user accounts
         for line in entry.lines:
             account = await get_account(line.account_id)
             if account and account.user_id:
-                entry_user_id = account.user_id
-                entry_account_type = account.account_type.value if hasattr(account.account_type, 'value') else account.account_type
-                user = await get_user(account.user_id)
-                entry_username = user.username if user and user.username else account.user_id[:16] + "..."
-                break
+                account_type = account.account_type.value if hasattr(account.account_type, 'value') else account.account_type
+
+                if account_type == 'equity':
+                    equity_account = (account.user_id, account_type, account)
+                    break  # Prioritize equity, stop searching
+                elif not other_user_account:
+                    other_user_account = (account.user_id, account_type, account)
+
+        # Use equity account if found, otherwise use other user account
+        selected_account = equity_account or other_user_account
+
+        if selected_account:
+            entry_user_id, entry_account_type, account_obj = selected_account
+            user = await get_user(entry_user_id)
+            entry_username = user.username if user and user.username else entry_user_id[:16] + "..."
 
         enriched_entries.append({
             **entry.dict(),