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/transcriptions.test.ts

@@ -0,0 +1,71 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+// Mock WebSocket for the backend store dependency (loaded transitively)
+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);
+
+vi.stubGlobal(
+  "fetch",
+  vi.fn(() =>
+    Promise.resolve({
+      ok: true,
+      json: () => Promise.resolve({}),
+    })
+  )
+);
+
+import { transcriptionStore } from "./transcriptions.svelte.ts";
+
+describe("transcriptions store", () => {
+  beforeEach(() => {
+    transcriptionStore.clearAll();
+  });
+
+  it("test_addTranscription", () => {
+    transcriptionStore.addTranscription({
+      text: "Hello world",
+      user_name: "TestUser",
+      timestamp: "12:00:00",
+    });
+
+    expect(transcriptionStore.items.length).toBe(1);
+    expect(transcriptionStore.items[0].text).toBe("Hello world");
+    expect(transcriptionStore.items[0].userName).toBe("TestUser");
+    expect(transcriptionStore.items[0].timestamp).toBe("12:00:00");
+    expect(transcriptionStore.items[0].isPreview).toBe(false);
+  });
+
+  it("test_clearAll", () => {
+    transcriptionStore.addTranscription({ text: "One" });
+    transcriptionStore.addTranscription({ text: "Two" });
+    expect(transcriptionStore.items.length).toBe(2);
+
+    transcriptionStore.clearAll();
+    expect(transcriptionStore.items.length).toBe(0);
+  });
+
+  it("test_getPlainText", () => {
+    transcriptionStore.addTranscription({
+      text: "Hello",
+      user_name: "Alice",
+      timestamp: "10:00",
+    });
+    transcriptionStore.addTranscription({
+      text: "World",
+      user_name: "Bob",
+      timestamp: "10:01",
+    });
+
+    const text = transcriptionStore.getPlainText();
+    expect(text).toContain("[10:00] Alice: Hello");
+    expect(text).toContain("[10:01] Bob: World");
+    // Lines separated by newline
+    expect(text.split("\n").length).toBe(2);
+  });
+});