Add unified setup script (configure.js) merging deploy + config wizard

Single-file Node.js CLI that orchestrates the full setup lifecycle:
- Interactive env var configuration with validation and smart defaults
- Postgres provisioning via Docker Compose with readiness polling
- Schema initialization (psql with docker exec fallback)
- npm dependency installation with 120s timeout
- Optional SQLite-to-Postgres data migration with retry logic
- Frontend build with smart skip on reconfiguration

Includes 84 tests: 50 property-based (fast-check) covering 19 correctness
properties, and 34 integration tests for filesystem and parsing flows.

backend/__tests__/config-wizard-masking.property.test.js

@@ -0,0 +1,64 @@
+/**
+ * Property-Based Tests: Config Wizard Sensitive Value Masking
+ *
+ * Feature: config-wizard
+ *
+ * Tests the maskSensitive display function from `configure.js`.
+ *
+ * Validates: Requirements 3.4
+ */
+
+const fc = require('fast-check');
+const { maskSensitive } = require('../../configure.js');
+
+// --- Property 4: Sensitive value masking ---
+describe('Property 4: Sensitive value masking', () => {
+  /**
+   * **Validates: Requirements 3.4**
+   *
+   * For any string value longer than 8 characters, maskSensitive returns
+   * first4 + '****' + last4. For any string value of 8 characters or fewer,
+   * maskSensitive returns the full value unchanged.
+   */
+  test('strings longer than 8 chars are masked as first4 + **** + last4', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ minLength: 9, maxLength: 200 }),
+        (value) => {
+          const result = maskSensitive('ANY_NAME', value);
+          const expected = value.slice(0, 4) + '****' + value.slice(-4);
+          return result === expected;
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  test('strings of 8 chars or fewer are returned unchanged', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ minLength: 0, maxLength: 8 }),
+        (value) => {
+          const result = maskSensitive('ANY_NAME', value);
+          return result === value;
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  test('masking behavior is independent of the variable name parameter', () => {
+    fc.assert(
+      fc.property(
+        fc.string({ minLength: 9, maxLength: 100 }),
+        fc.string({ minLength: 1, maxLength: 50 }),
+        (value, name) => {
+          const result = maskSensitive(name, value);
+          const expected = value.slice(0, 4) + '****' + value.slice(-4);
+          return result === expected;
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+});