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/file-extension.test.ts

@@ -0,0 +1,34 @@
+import { describe, it, expect } from "vitest";
+import * as fs from "node:fs";
+import * as path from "node:path";
+
+describe("store file extensions", () => {
+  it("test_store_files_use_svelte_ts_extension", () => {
+    const storesDir = path.resolve(__dirname);
+    const files = fs.readdirSync(storesDir);
+
+    // Find .ts files that are NOT .svelte.ts and NOT test files
+    const plainTsFiles = files.filter(
+      (f) =>
+        f.endsWith(".ts") &&
+        !f.endsWith(".svelte.ts") &&
+        !f.endsWith(".test.ts")
+    );
+
+    for (const file of plainTsFiles) {
+      const content = fs.readFileSync(path.join(storesDir, file), "utf-8");
+      expect(content).not.toMatch(
+        /\$state\s*[<(]/,
+        `${file} uses $state() but does not have .svelte.ts extension`
+      );
+      expect(content).not.toMatch(
+        /\$derived\s*[<(]/,
+        `${file} uses $derived() but does not have .svelte.ts extension`
+      );
+      expect(content).not.toMatch(
+        /\$effect\s*[<(]/,
+        `${file} uses $effect() but does not have .svelte.ts extension`
+      );
+    }
+  });
+});