Finalize Dexie-to-SQLite migration prep: docs, circular dep removal, SQL helpers, tests

- Removed all vestigial Dexie/USE_DEXIE_DB references from code and docs
- Centralized DB logic in PlatformServiceMixin; resolved logger/databaseUtil circular dependency
- Modularized SQL helpers (`$generateInsertStatement`, `$generateUpdateStatement`) and added unit tests
- Created/updated migration tracking docs and helper script for cross-machine progress
- Confirmed all lint/type checks and tests pass; ready for systematic file migration

doc/secure-storage-implementation.md

@@ -130,10 +130,9 @@ async function getAccount(did: string): Promise<Account | undefined> {
     [did]
   );
 
-  // Fallback to Dexie if needed
-  if (USE_DEXIE_DB) {
-    account = await db.accounts.get(did);
-  }
+  // Fallback to Dexie if needed (migration period only)
+  // Note: This fallback is only used during the migration period
+  // and will be removed once migration is complete
 
   return account;
    }
@@ -156,10 +155,9 @@ When converting from Dexie.js to SQL-based implementation, follow these patterns
    );
    result = databaseUtil.mapQueryResultToValues(result);
    
-   // Fallback to Dexie if needed
-   if (USE_DEXIE_DB) {
-     result = await db.table.where("field").equals(value).first();
-   }
+   // Fallback to Dexie if needed (migration period only)
+   // Note: This fallback is only used during the migration period
+   // and will be removed once migration is complete
    ```
 
 2. **Update Operations**
@@ -180,10 +178,9 @@ When converting from Dexie.js to SQL-based implementation, follow these patterns
      [changes.field1, changes.field2, id]
    );
 
-   // Fallback to Dexie if needed
-   if (USE_DEXIE_DB) {
-     await db.table.where("id").equals(id).modify(changes);
-   }
+   // Fallback to Dexie if needed (migration period only)
+   // Note: This fallback is only used during the migration period
+   // and will be removed once migration is complete
    ```
 
 3. **Insert Operations**
@@ -199,10 +196,9 @@ When converting from Dexie.js to SQL-based implementation, follow these patterns
    const sql = `INSERT INTO table (${columns.join(', ')}) VALUES (${placeholders})`;
    await platform.dbExec(sql, values);
 
-   // Fallback to Dexie if needed
-   if (USE_DEXIE_DB) {
-     await db.table.add(item);
-   }
+   // Fallback to Dexie if needed (migration period only)
+   // Note: This fallback is only used during the migration period
+   // and will be removed once migration is complete
    ```
 
 4. **Delete Operations**
@@ -214,10 +210,9 @@ When converting from Dexie.js to SQL-based implementation, follow these patterns
    const platform = PlatformServiceFactory.getInstance();
    await platform.dbExec("DELETE FROM table WHERE id = ?", [id]);
 
-   // Fallback to Dexie if needed
-   if (USE_DEXIE_DB) {
-     await db.table.where("id").equals(id).delete();
-   }
+   // Fallback to Dexie if needed (migration period only)
+   // Note: This fallback is only used during the migration period
+   // and will be removed once migration is complete
    ```
 
 5. **Result Processing**
@@ -230,10 +225,9 @@ When converting from Dexie.js to SQL-based implementation, follow these patterns
    let items = await platform.dbQuery("SELECT * FROM table");
    items = databaseUtil.mapQueryResultToValues(items);
 
-   // Fallback to Dexie if needed
-   if (USE_DEXIE_DB) {
-     items = await db.table.toArray();
-   }
+   // Fallback to Dexie if needed (migration period only)
+   // Note: This fallback is only used during the migration period
+   // and will be removed once migration is complete
    ```
 
 6. **Using Utility Methods**
@@ -255,9 +249,9 @@ await databaseUtil.logConsoleAndDb(message, showInConsole);
 Key Considerations:
 - Always use `databaseUtil.mapQueryResultToValues()` to process SQL query results
 - Use utility methods from `db/index.ts` when available instead of direct SQL
-- Keep Dexie fallbacks wrapped in `if (USE_DEXIE_DB)` checks
+- Keep Dexie fallbacks wrapped in migration period checks
 - For queries that return results, use `let` variables to allow Dexie fallback to override
-- For updates/inserts/deletes, execute both SQL and Dexie operations when `USE_DEXIE_DB` is true
+- For updates/inserts/deletes, execute both SQL and Dexie operations during migration period
 
 Example Migration:
 ```typescript
@@ -285,8 +279,8 @@ Remember to:
 
   - For creates & updates & deletes, the duplicate code is fine.
 
-  - For queries where we use the results, make the setting from SQL into a 'let' variable, then wrap the Dexie code in a check for USE_DEXIE_DB from app.ts and if
-it's true then use that result instead of the SQL code's result.
+  - For queries where we use the results, make the setting from SQL into a 'let' variable, then wrap the Dexie code in a migration period check and if
+it's during migration then use that result instead of the SQL code's result.
 
 - Consider data migration needs, and warn if there are any potential migration problems