Add Cloud Agent environment config for neoswift build

[hihaar]

What

Adds a Cursor Cloud Agent environment definition so fresh agents boot ready to build and test neoswift on Linux.

• .cursor/environment.json — repo-file managed config (user: ubuntu, install: bash .cursor/cloud-install.sh) that declares neoswift-externals and rustfsd as repositoryDependencies.
• .cursor/cloud-install.sh — idempotent install script that provisions the CI-proven Linux toolchain and performs an end-to-end build of neoswift.

Why

This run started with no linked/dashboard environment (greenfield). Booting agents therefore lacked Qt, Conan, and Ninja, so neoswift could not be built. This commits the setup as version-controlled, repo-file-managed configuration.

Install script behavior

Reproduces the working Linux path from .github/workflows/build.yml:

1. System packages: build-essential cmake ninja-build pkg-config dbus-x11 libdbus-1-dev libglu1-mesa-dev libgl1-mesa-dev libpulse-dev libxkbcommon-dev libxcb-cursor0
2. Python tooling: conan, aqtinstall, requests (pip --user)
3. Qt 6.10.1 linux_gcc_64 with qtmultimedia + qtwebsockets via aqtinstall → /opt/Qt
4. Rust stable toolchain (rustfsd requires ≥ 1.88)
5. neoswift bootstrap: init third_party/msgpack submodule, optionally symlink neoswift-externals → third_party/externals, conan install (Debug) + cmake --preset dev-debug + build
6. cargo fetch for rustfsd

The dev-debug preset disables VATSIM auth and xswiftbus, so no secrets and no ssh-only submodule (xplanemp2) are required. All helper-repo steps are guarded so the neoswift build succeeds even if the helper repos are absent.

Validation (on this VM, same base image)

Check	Result
neoswift build (dev-debug, 1042 targets)	Succeeded
neoswift ctest	35/35 passed
rustfsd cargo build --release	Succeeded
rustfsd cargo test	32/32 passed
Install script re-run	Idempotent (Qt skipped, incremental no-op build, clean git trees)

Toolchain: cmake 3.28.3 · ninja 1.11.1 · gcc 13.3.0 · Qt 6.10.1 · conan 2.31.2 · rustc 1.98.0

neoswift-env-validation.log

Notes

• Agent-triggered draft-build verification (fresh cloud agent) could not run: this greenfield run has no linked environment, and the build tool will only build the repo-file config once it is present on the default branch. Merging this PR resolves that; subsequent Cloud Agents (and draft builds) will use this config.

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