feat: initial myprimal MQTT bridge service

Dynamic MySolem/MyIndygo IoT bridge with MQTT, Home Assistant
autodiscovery, and Homebridge EasyMQTT compatibility.

- Device discovery via MySolem API on startup (all modules/inputs/outputs)
- Configurable poll engine (fast/normal/slow buckets, per-input overrides)
- MQTT retained state publishing + HA autodiscovery payloads
- Unified manual command routing (linesControl vs sendManualModuleCommand)
- Runtime config via MQTT $config/set, persisted to config.json
- Expression override system (API-provided > hardcoded > passthrough)
- Minimal REST API: /health, /state, /control, /rediscover
- Docker deployment (Dockerfile + docker-compose.yml)
- 38 unit tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/config.js

@@ -0,0 +1,57 @@
+'use strict';
+const fs = require('fs');
+const path = require('path');
+const { EventEmitter } = require('events');
+
+const CONFIG_PATH = process.env.MYPRIMAL_CONFIG_PATH || path.join(__dirname, '..', 'config.json');
+
+const DEFAULTS = {
+  poll: {
+    fast:      parseInt(process.env.POLL_FAST)   || 60,
+    normal:    parseInt(process.env.POLL_NORMAL) || 300,
+    slow:      parseInt(process.env.POLL_SLOW)   || 900,
+    overrides: {},
+  },
+  expressions: {},  // inputId → expression string override, e.g. "value/10"
+};
+
+const emitter = new EventEmitter();
+let _config = deepMerge({}, DEFAULTS);
+
+function deepMerge(target, source) {
+  for (const key of Object.keys(source || {})) {
+    if (source[key] && typeof source[key] === 'object' && !Array.isArray(source[key])) {
+      target[key] = deepMerge(target[key] || {}, source[key]);
+    } else {
+      target[key] = source[key];
+    }
+  }
+  return target;
+}
+
+function loadConfig() {
+  if (fs.existsSync(CONFIG_PATH)) {
+    try {
+      const saved = JSON.parse(fs.readFileSync(CONFIG_PATH, 'utf8'));
+      _config = deepMerge(deepMerge({}, DEFAULTS), saved);
+    } catch (e) {
+      console.warn('[config] Failed to parse config.json, using defaults:', e.message);
+    }
+  }
+}
+
+function saveConfig() {
+  fs.writeFileSync(CONFIG_PATH, JSON.stringify(_config, null, 2));
+}
+
+function getConfig() {
+  return _config;
+}
+
+function patchConfig(patch) {
+  _config = deepMerge(_config, patch);
+  saveConfig();
+  emitter.emit('change', _config);
+}
+
+module.exports = { loadConfig, getConfig, patchConfig, on: emitter.on.bind(emitter) };