feat(engine): replace vague error strings with structured get_engine_status diagnostics

Add a single Rust command returning per-engine structured status with
resolved path, version, error context, stderr tail, and remediation hints.

- Aria2: binary check, daemon startup error, RPC readiness, live stderr capture
- yt-dlp: binary check, onedir layout validation (_internal/Python.framework)
- FFmpeg / Deno: binary check, version parse
- UI: Ready/Error badge + expandable technical detail panel
- Old test_* commands kept for backward compatibility

src/bindings/EngineStatusItem.ts

@@ -0,0 +1,3 @@
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+
+export type EngineStatusItem = { name: string, kind: string, expected_sidecar: string, resolved_path: string | null, version: string | null, ready: boolean, error: string | null, stderr_tail: string | null, remediation_hint: string | null, rpc_port: number | null, daemon_alive: boolean | null, rpc_ready: boolean | null, last_stderr_tail: string | null, expects_internal_dir: boolean | null, has_internal_dir: boolean | null, has_python_framework: boolean | null, };

src/bindings/EngineStatusResult.ts

@@ -0,0 +1,4 @@
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+import type { EngineStatusItem } from "./EngineStatusItem";
+
+export type EngineStatusResult = { engines: Array<EngineStatusItem>, };