Add test suite (63 tests) and CI workflow, fix Settings API bugs

Test suite covering all three layers:

Python backend (25 tests):
- AppController: state machine, start/stop, callbacks, settings reload
- API server: REST endpoints, config CRUD, status, devices
- Config: dot-notation get/set, persistence, nested paths
- Main headless: ready event port format validation

Svelte frontend (14 tests via Vitest):
- Backend store: exported properties/methods, port derivation, URLs
- Config store: method names (fetchConfig not loadConfig), defaults
- Transcriptions store: add/clear/plaintext
- File extension regression: ensures $state runes only in .svelte.ts

Rust sidecar (24 tests via cargo test):
- Platform/arch detection, asset name construction
- Ready event deserialization (with extra fields tolerance)
- Path construction, version read/write, old version cleanup
- Zip extraction, SidecarManager lifecycle

CI workflow (.gitea/workflows/test.yml):
- Runs on push to main and PRs
- Three parallel jobs: Python, Frontend, Rust

Also fixes three bugs found during test planning:
- Settings: /api/check-updates -> GET /api/check-update
- Settings: /api/remote/login -> /api/login
- Settings: /api/remote/register -> /api/register

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/stores/backend.test.ts

@@ -0,0 +1,77 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { backendStore } from "./backend.svelte.ts";
+
+// Mock WebSocket globally so the store module can reference it
+class MockWebSocket {
+  onopen: ((ev: Event) => void) | null = null;
+  onclose: ((ev: CloseEvent) => void) | null = null;
+  onmessage: ((ev: MessageEvent) => void) | null = null;
+  onerror: ((ev: Event) => void) | null = null;
+  close = vi.fn();
+}
+vi.stubGlobal("WebSocket", MockWebSocket);
+
+// Mock fetch to prevent real network calls
+vi.stubGlobal(
+  "fetch",
+  vi.fn(() =>
+    Promise.resolve({
+      ok: true,
+      json: () => Promise.resolve({}),
+    })
+  )
+);
+
+describe("backend store", () => {
+  beforeEach(() => {
+    backendStore.disconnect();
+    backendStore.setPort(8081);
+  });
+
+  it("test_exports_expected_properties", () => {
+    expect(backendStore).toHaveProperty("port");
+    expect(backendStore).toHaveProperty("connectionState");
+    expect(backendStore).toHaveProperty("connected");
+    expect(backendStore).toHaveProperty("appState");
+    expect(backendStore).toHaveProperty("stateMessage");
+    expect(backendStore).toHaveProperty("deviceInfo");
+    expect(backendStore).toHaveProperty("version");
+    expect(backendStore).toHaveProperty("lastError");
+    expect(backendStore).toHaveProperty("apiBaseUrl");
+    expect(backendStore).toHaveProperty("wsUrl");
+    expect(backendStore).toHaveProperty("obsUrl");
+    expect(backendStore).toHaveProperty("syncUrl");
+  });
+
+  it("test_exports_expected_methods", () => {
+    expect(typeof backendStore.setPort).toBe("function");
+    expect(typeof backendStore.connect).toBe("function");
+    expect(typeof backendStore.disconnect).toBe("function");
+    expect(typeof backendStore.apiUrl).toBe("function");
+    expect(typeof backendStore.apiFetch).toBe("function");
+    expect(typeof backendStore.apiGet).toBe("function");
+    expect(typeof backendStore.apiPost).toBe("function");
+    expect(typeof backendStore.apiPut).toBe("function");
+  });
+
+  it("test_obsUrl_derives_from_port", () => {
+    backendStore.setPort(8081);
+    expect(backendStore.obsUrl).toBe("http://localhost:8080");
+  });
+
+  it("test_apiBaseUrl_uses_port", () => {
+    backendStore.setPort(8081);
+    expect(backendStore.apiBaseUrl).toBe("http://localhost:8081");
+  });
+
+  it("test_wsUrl_uses_port", () => {
+    backendStore.setPort(8081);
+    expect(backendStore.wsUrl).toBe("ws://localhost:8081/ws/control");
+  });
+
+  it("test_initial_state", () => {
+    // After disconnect() in beforeEach, state should be disconnected
+    expect(backendStore.connectionState).toBe("disconnected");
+    expect(backendStore.appState).toBe("initializing");
+  });
+});