ci: move desktop cargo check out of github actions

AGENTS.md

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+# openconcho Agent Notes
+
+## CI policy
+
+- PR CI only runs the web checks.
+- Rust/Tauri compile-check is local-only for now because the Linux dependency setup on GitHub Actions is too slow for routine PR validation.
+
+## Required local preflight
+
+- Before pushing any change under `packages/desktop/**` or `packages/desktop/src-tauri/**`, run:
+  - `pnpm --filter @openconcho/desktop cargo-check`
+
+## Useful commands
+
+- `make ci-web` — matches current PR CI
+- `pnpm --filter @openconcho/desktop cargo-check` — local desktop compile check