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>

client/tests/test_config.py

@@ -0,0 +1,78 @@
+"""Tests for client.config.Config."""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+# Ensure project root is on path
+project_root = Path(__file__).resolve().parent.parent.parent
+sys.path.insert(0, str(project_root))
+
+from client.config import Config
+
+
+@pytest.fixture
+def cfg(tmp_path):
+    """A Config backed by a temp file so we never touch the real user config."""
+    return Config(config_path=str(tmp_path / "test_config.yaml"))
+
+
+# ── dot-notation get ────────────────────────────────────────────────
+
+
+def test_dot_notation_get(cfg):
+    """Config.get should traverse nested dicts using dot-separated keys."""
+    cfg.config = {"audio": {"sample_rate": 16000}}
+    assert cfg.get("audio.sample_rate") == 16000
+
+
+# ── dot-notation set ────────────────────────────────────────────────
+
+
+def test_dot_notation_set(cfg):
+    """Config.set should create/update nested values via dot-separated keys."""
+    cfg.set("audio.sample_rate", 44100)
+    assert cfg.config["audio"]["sample_rate"] == 44100
+
+    # Also readable via .get
+    assert cfg.get("audio.sample_rate") == 44100
+
+
+# ── missing key returns default ─────────────────────────────────────
+
+
+def test_missing_key_returns_default(cfg):
+    """Accessing a nonexistent key should return the supplied default."""
+    assert cfg.get("nonexistent.path", "fallback") == "fallback"
+    assert cfg.get("also.missing") is None  # default default is None
+
+
+# ── nested set creates intermediate dicts ───────────────────────────
+
+
+def test_nested_set_creates_path(cfg):
+    """Setting a deeply nested key should create all intermediate dicts."""
+    cfg.config = {}
+    cfg.set("a.b.c.d", 42)
+
+    assert cfg.config["a"]["b"]["c"]["d"] == 42
+    assert cfg.get("a.b.c.d") == 42
+
+
+# ── save and reload round-trip ──────────────────────────────────────
+
+
+def test_save_and_reload(tmp_path):
+    """Values persisted via save() should survive a fresh Config load."""
+    config_file = str(tmp_path / "roundtrip.yaml")
+
+    # Create and populate
+    cfg1 = Config(config_path=config_file)
+    cfg1.set("user.name", "TestUser")
+    cfg1.set("transcription.model", "tiny.en")
+
+    # Load a fresh instance from the same file
+    cfg2 = Config(config_path=config_file)
+    assert cfg2.get("user.name") == "TestUser"
+    assert cfg2.get("transcription.model") == "tiny.en"