docs: add installation pages for bonsaiviewer and ifcviewer

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/bonsaiviewer/docs/index.rst

@@ -38,6 +38,7 @@ files and viewer-oriented formats such as ``.ifcview`` and ``.rdbview``.
       :caption: Contents
       :maxdepth: 2
 
+      installation
       connectors/index
       debug-output
       env-vars

src/bonsaiviewer/docs/installation.rst

@@ -0,0 +1,93 @@
+Developer installation
+======================
+
+This page is for developers who want to compile Bonsai Viewer from source.
+End users should install a packaged release rather than building it themselves.
+
+Bonsai Viewer is a native C++ application (Qt6 + WebGPU) built together with
+the rest of IfcOpenShell. It is not a Blender add-on, so — unlike Bonsai —
+there is no "live development" symlink workflow: you rebuild the binary after
+changing the code.
+
+System requirements
+-------------------
+
+- A 64-bit Linux, macOS, or Windows host.
+- A C++17 compiler, CMake 3.21 or newer, and Ninja.
+- Qt6 with OpenGL 4.5 support (``BUILD_BONSAIVIEWER`` requires it).
+- The IfcOpenShell geometry dependencies (Boost, OpenCASCADE, Eigen, CGAL,
+  GMP/MPFR) and the viewer's sidecar/kernel dependencies (RocksDB, zstd,
+  Manifold).
+
+The viewer is built on the IfcViewer library. If you want to build your own
+application on that library instead of the ready-made Bonsai Viewer, see
+"Building with IfcViewer" in the IfcOpenShell documentation (under
+``src/ifcopenshell-python/docs/ifcviewer``).
+
+Batteries-included build
+------------------------
+
+The simplest way to get a working build — and the one continuous integration
+uses — is ``nix/build-all.py``. It downloads and compiles every dependency
+(including Qt6) and then Bonsai Viewer itself. From the repository root:
+
+.. code-block:: bash
+
+    BUILD_BONSAIVIEWER=ON python3 ./nix/build-all.py
+
+Setting ``BUILD_BONSAIVIEWER=ON`` pulls in the ``BonsaiViewer`` and ``qt6``
+targets along with their dependencies. This is self-contained but slow on a
+cold checkout, because it builds the whole dependency stack from source. The
+finished executable lands under the platform build tree, e.g.
+``build/<system>/<arch>/install/ifcopenshell/bin/BonsaiViewer``.
+
+Direct CMake build
+------------------
+
+If you already have Qt6 and the geometry dependencies available (for example
+from a previous ``build-all.py`` run), you can configure and build the app
+directly against them. ``BUILD_BONSAIVIEWER`` implies
+``BUILD_BONSAIVIEWER_WGPU``, so the WebGPU backend is built automatically:
+
+.. code-block:: bash
+
+    cmake -S cmake -B build-viewer \
+        -G Ninja \
+        -DCMAKE_BUILD_TYPE=Debug \
+        -DBUILD_BONSAIVIEWER=ON \
+        -DCMAKE_PREFIX_PATH="/path/to/deps"
+
+    cmake --build build-viewer --target BonsaiViewer
+
+Set ``-DCMAKE_PREFIX_PATH`` to a ``;``-separated list of your dependency
+install prefixes (Boost, OpenCASCADE, CGAL, Eigen, GMP/MPFR, Manifold,
+RocksDB, zstd) so CMake can find them. Other useful targets are ``IfcViewer``
+(the shared engine library) and ``IfcViewerMinimal`` (a small standalone
+frontend).
+
+To also build the C++ unit tests for the viewer core, add
+``-DBUILD_BONSAIVIEWER_TESTS=ON`` and run them with CTest.
+
+Running from source
+-------------------
+
+Run the built binary directly:
+
+.. code-block:: bash
+
+    ./build-viewer/bonsaiviewer/BonsaiViewer
+
+Runtime behaviour can be tuned with environment variables (logging, geometry
+kernel selection, and other diagnostics) — see :doc:`env-vars` and
+:doc:`debug-output`. For an overview of how the rendering and viewport code is
+organised, see :doc:`viewport_architecture`.
+
+The Autodesk connector
+----------------------
+
+Bonsai Viewer discovers connectors at ``<BonsaiViewer dir>/connectors``. The
+Autodesk connector is a separate Rust crate under ``src/bonsaiviewer-autodesk``
+and is built with ``cargo`` (its packaging step is run by
+``src/bonsaiviewer-autodesk/packaging/build.py``). For a local debug build,
+symlink the built connector into the viewer's ``connectors`` directory so the
+running app can find it. See :doc:`connectors/index` for details.