feat(FN-3396): bundle Cursor CLI as a plugin provider with dashboard auth w

Merges FN-3396's full Cursor CLI provider integration (Steps 1–4): defines a CLI-backed provider contract, adds the `fusion-plugin-cursor-runtime` plugin package with process management and runtime probes, wires dashboard auth flows and UI (ProviderCard, onboarding modal, settings), and bundles the

Fusion-Task-Id: FN-3396

plugins/fusion-plugin-cursor-runtime/README.md

@@ -0,0 +1,14 @@
+# fusion-plugin-cursor-runtime
+
+Cursor CLI-backed provider/runtime plugin for Fusion.
+
+## Contract summary
+
+- Provider ID: `cursor-cli`
+- Binary probes: `cursor-agent`, then `cursor`
+- Expected failure states: missing binary, missing Cursor IDE install, locked macOS keychain, unauthenticated runtime
+- Model discovery: dynamic command probing (`models --json`, fallbacks) with dedupe + fallback metadata
+
+## Notes
+
+Status/auth and model discovery behavior follows `docs/cursor-cli-contract.md`.