Add Aider provider with OpenRouter support and per-provider sidecar routing

- Add aider-runner.ts sidecar that spawns aider CLI in non-interactive mode
- Add Aider provider metadata with OpenRouter model presets
- Add aider-messages.ts adapter for Aider event format
- Refactor SidecarManager from single-process to per-provider process management
  with lazy startup on first query and session→provider routing
- Add openrouter_api_key to secrets system (keyring storage)
- Inject OPENROUTER_API_KEY from secrets into Aider agent environment
- Register Aider in provider registry, build pipeline, and resource bundle

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

v2/src-tauri/src/secrets.rs

@@ -14,6 +14,7 @@ const KEYS_META: &str = "__bterminal_keys__";
 pub const KNOWN_KEYS: &[&str] = &[
     "anthropic_api_key",
     "openai_api_key",
+    "openrouter_api_key",
     "github_token",
     "relay_token",
 ];

v2/src-tauri/tauri.conf.json

@@ -46,6 +46,7 @@
     ],
     "resources": [
       "../sidecar/dist/claude-runner.mjs",
+      "../sidecar/dist/aider-runner.mjs",
       "../../btmsg",
       "../../bttask"
     ],