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.

helper/import_beancount.py

@@ -153,9 +153,10 @@ class AccountLookup:
         Special handling for user-specific accounts:
         - "Liabilities:Payable:Pat" -> looks up Pat's user_id and finds their Castle payable account
         - "Assets:Receivable:Pat" -> looks up Pat's user_id and finds their Castle receivable account
+        - "Equity:Pat" -> looks up Pat's user_id and finds their Castle equity account
 
         Args:
-            account_name: Beancount account name (e.g., "Expenses:Food:Supplies", "Liabilities:Payable:Pat", "Assets:Receivable:Pat")
+            account_name: Beancount account name (e.g., "Expenses:Food:Supplies", "Liabilities:Payable:Pat", "Assets:Receivable:Pat", "Equity:Pat")
 
         Returns:
             Castle account UUID or None if not found
@@ -204,6 +205,28 @@ class AccountLookup:
                         f"Please configure the wallet for user ID: {user_id}"
                     )
 
+        # Check if this is an Equity:<name> account
+        # Map Beancount Equity:Pat to Castle Equity:User-<id>
+        elif account_name.startswith("Equity:"):
+            user_name = extract_user_from_user_account(account_name)
+            if user_name:
+                # Look up user's actual user_id
+                user_id = USER_MAPPINGS.get(user_name)
+                if user_id:
+                    # Find this user's equity account
+                    # This is the Equity:User-<id> account in Castle
+                    if user_id in self.accounts_by_user:
+                        equity_account_id = self.accounts_by_user[user_id].get('equity')
+                        if equity_account_id:
+                            return equity_account_id
+
+                    # If not found, provide helpful error
+                    raise ValueError(
+                        f"User '{user_name}' (ID: {user_id}) does not have an equity account.\n"
+                        f"Equity eligibility must be enabled for this user in Castle.\n"
+                        f"Please enable equity for user ID: {user_id}"
+                    )
+
         # Normal account lookup by name
         return self.accounts.get(account_name)
 
@@ -332,11 +355,12 @@ def parse_beancount_transaction(txn_text: str) -> Optional[Dict]:
 
 def extract_user_from_user_account(account_name: str) -> Optional[str]:
     """
-    Extract user name from user-specific accounts (Payable or Receivable).
+    Extract user name from user-specific accounts (Payable, Receivable, or Equity).
 
     Examples:
         "Liabilities:Payable:Pat" -> "Pat"
         "Assets:Receivable:Alice" -> "Alice"
+        "Equity:Pat" -> "Pat"
         "Expenses:Food" -> None
 
     Returns:
@@ -350,6 +374,10 @@ def extract_user_from_user_account(account_name: str) -> Optional[str]:
         parts = account_name.split(":")
         if len(parts) >= 3:
             return parts[2]
+    elif account_name.startswith("Equity:"):
+        parts = account_name.split(":")
+        if len(parts) >= 2:
+            return parts[1]
     return None
 
 def determine_user_id(postings: list) -> Optional[str]:
@@ -386,8 +414,11 @@ def convert_to_castle_entry(parsed: dict, btc_eur_rate: float, account_lookup: A
     if not user_id:
         raise ValueError(
             f"Could not determine user ID for transaction.\n"
-            f"Transactions must have a Liabilities:Payable:<name> or Assets:Receivable:<name> account.\n"
-            f"Examples: Liabilities:Payable:Pat, Assets:Receivable:Pat"
+            f"Transactions must have a user-specific account:\n"
+            f"  - Liabilities:Payable:<name> (for payables)\n"
+            f"  - Assets:Receivable:<name> (for receivables)\n"
+            f"  - Equity:<name> (for equity)\n"
+            f"Examples: Liabilities:Payable:Pat, Assets:Receivable:Pat, Equity:Pat"
         )
 
     # Build entry lines