modules: wire tool-runtime app credentials as own-secrets

The six modules that run a mesh-<mod> tool-runtime sidecar read an app
credential from an env var the manifest never provided, so the sidecar
crash-looped in the whole-mesh dry-run (e.g. "no Plex token — set
MESH_PLEX_TOKEN"). These are operator-set app secrets, so deliver them the
same way cloudflare-dns delivers its API token: an own-secret file mounted
read-only, with a MESH_<APP>_*_FILE env pointing at the mount, and the
runtime code preferring that file (falling back to the existing env so
nothing regresses).

- plex: own-secret token -> /run/secrets/token, MESH_PLEX_TOKEN_FILE
- bazarr: own-secret api-key -> /run/secrets/api-key, MESH_BAZARR_API_KEY_FILE
- ombi: own-secret api-key -> /run/secrets/api-key, MESH_OMBI_API_KEY_FILE
- home-assistant: own-secret token -> /run/secrets/token, MESH_HOMEASSISTANT_TOKEN_FILE
- nzbget: own-secret password -> /run/secrets/password, MESH_NZBGET_PASSWORD_FILE (URL stays plain env)
- qbittorrent: own-secret password -> /run/secrets/password, MESH_QBITTORRENT_PASSWORD_FILE (URL stays plain env)

The operator now completes each with `secret accept <node> <module> <name> --from <file>`.
tsc passes for all six.

modules/home-assistant/client.ts

@@ -27,6 +27,14 @@ function meshConfig(file?: string): Record<string, string> {
   catch { return {}; }
 }
 
+/** Read a secret the mesh mounted at a file path (an own-secret delivered by `secret accept`);
+ *  absent or unreadable yields undefined so callers fall back rather than crash. */
+function readSecret(file?: string): string | undefined {
+  if (!file) return undefined;
+  try { return readFileSync(file, "utf8").trim(); }
+  catch { return undefined; }
+}
+
 export class HomeAssistantClient {
   readonly baseUrl: string;
 
@@ -45,7 +53,7 @@ export class HomeAssistantClient {
   static fromEnv(env: NodeJS.ProcessEnv = process.env): HomeAssistantClient {
     const cfg = meshConfig(env.MESH_HOMEASSISTANT_CONFIG_FILE);
     const url = cfg.url ?? env.MESH_HOMEASSISTANT_URL ?? `http://127.0.0.1:${env.HOMEASSISTANT_PORT ?? "8123"}`;
-    const token = cfg.token ?? env.MESH_HOMEASSISTANT_TOKEN;
+    const token = cfg.token ?? readSecret(env.MESH_HOMEASSISTANT_TOKEN_FILE) ?? env.MESH_HOMEASSISTANT_TOKEN;
     if (!token) throw new Error("no Home Assistant token — set MESH_HOMEASSISTANT_TOKEN");
     return new HomeAssistantClient(url, token);
   }