Remember the last-used GnuCash account per file

AppConfig now keeps a gnucash_last_accounts map (file path -> account
guid). When the import dialog opens a file it already knows, it
auto-selects whichever account was picked last time for that specific
file instead of always defaulting to the first one alphabetically;
picking a different account updates and persists the mapping right away.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/ccma/config.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import json
 import math
 import os
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from pathlib import Path
 from typing import TYPE_CHECKING
 
@@ -18,6 +18,7 @@ if TYPE_CHECKING:
 class AppConfig:
     store_path: str = ""
     gnucash_path: str = ""
+    gnucash_last_accounts: dict[str, str] = field(default_factory=dict)
     theme_mode: str = "dark"
     run_housekeeper_on_startup: bool = True
     splash_minimum_seconds: float = 5.0
@@ -43,6 +44,7 @@ class AppConfig:
                 "schema_version": 1,
                 "store_path": self.store_path,
                 "gnucash_path": self.gnucash_path,
+                "gnucash_last_accounts": self.gnucash_last_accounts,
                 "theme_mode": self.theme_mode,
                 "run_housekeeper_on_startup": self.run_housekeeper_on_startup,
                 "splash_minimum_seconds": _non_negative_float(self.splash_minimum_seconds, 5.0),
@@ -97,9 +99,16 @@ def load_config() -> AppConfig:
         monitor_bounds = None
         if isinstance(monitor_raw, list) and len(monitor_raw) == 4:
             monitor_bounds = tuple(int(value) for value in monitor_raw)
+        last_accounts_raw = data.get("gnucash_last_accounts")
+        gnucash_last_accounts = (
+            {str(key): str(value) for key, value in last_accounts_raw.items()}
+            if isinstance(last_accounts_raw, dict)
+            else {}
+        )
         return AppConfig(
             store_path=store_override or str(data.get("store_path", "")),
             gnucash_path=str(data.get("gnucash_path", "")),
+            gnucash_last_accounts=gnucash_last_accounts,
             theme_mode=str(data.get("theme_mode", "dark")),
             run_housekeeper_on_startup=bool(data.get("run_housekeeper_on_startup", True)),
             splash_minimum_seconds=_non_negative_float(data.get("splash_minimum_seconds", 5.0), 5.0),