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

src/test/PlatformServiceMixin.test.ts

@@ -0,0 +1,32 @@
+import {
+  generateInsertStatement,
+  generateUpdateStatement,
+} from "@/utils/sqlHelpers";
+
+describe("sqlHelpers SQL Statement Generation", () => {
+  it("generates correct INSERT statement", () => {
+    const contact = {
+      name: "Alice",
+      age: 30,
+      isActive: true,
+      tags: ["friend"],
+    };
+    const { sql, params } = generateInsertStatement(contact, "contacts");
+    expect(sql).toBe(
+      "INSERT INTO contacts (name, age, isActive, tags) VALUES (?, ?, ?, ?)",
+    );
+    expect(params).toEqual(["Alice", 30, 1, JSON.stringify(["friend"])]);
+  });
+
+  it("generates correct UPDATE statement", () => {
+    const changes = { name: "Bob", isActive: false };
+    const { sql, params } = generateUpdateStatement(
+      changes,
+      "contacts",
+      "id = ?",
+      [42],
+    );
+    expect(sql).toBe("UPDATE contacts SET name = ?, isActive = ? WHERE id = ?");
+    expect(params).toEqual(["Bob", 0, 42]);
+  });
+});