ci: add Blender smoke-test workflow (runs examples in real Blender)

[TMHSDigital]

Summary

Adds a durable gate that executes the snippets' and skills' headline examples inside real Blender — headless, on the current stable (5.1.x) and active LTS (4.5.x) — and fails on any error or empty-output assertion. Every real bug this cycle (EEVEE-id inversion, slotted-actions boundary, driver TypeError, dead SDF link) passed py_compile and only surfaced by running in Blender; this closes that gap.

Adds only new files — no existing workflow touched, no shipped content changed, counts unchanged (12/6/2/17):

• .github/workflows/blender-smoke.yml
• tests/smoke/run_smoke.py (in-process content checks, self-contained — copies example code, does not import skills/snippets)
• tests/smoke/{tmpl_gltf.py,tmpl_render.py,make_input.py} (template fixtures)

What it asserts (CONTENT, not "no exception")

• F1 driver: attaches AND location.z strictly increases across frames.
• F2 SDF remesh: GridToMesh link is valid AND yields >0 vertices.
• EEVEE: version-branch helper assigns the id that exists on this build (the inversion guard); a 1-frame render is non-black (EEVEE where a GPU exists, else Cycles fallback — runner-safe).
• slotted actions: correct branch per version; legacy action.fcurves present on 4.5 / AttributeError on 5.x.
• save_pre: handler arg is a filepath string. mesh: foreach roundtrip; SUBSURF eval vcount > base.
• templates (subprocess): glTF exit 0 + valid .glb; no-mesh exit 2; render exit 0.

The driver exits non-zero naming the first failing example — including on any unhandled exception, since blender --background otherwise exits 0 after printing a traceback (the documented headless gotcha).

Triggers & matrix

workflow_dispatch + weekly schedule (Mon 07:00 UTC) + pull_request on main (gates future example changes). Matrix resolves the latest 5.1.x and 4.5.x point release from download.blender.org and fails loudly if a build can't be fetched; a version guard asserts the downloaded build matches the matrix series. timeout-minutes: 30.

Verification (done before this PR)

• Local green, both builds: ALL SMOKE CHECKS PASSED exit 0 on Blender 5.1.1 and 4.5.10 LTS, plus glTF exit 0 / no-mesh exit 2 / render exit 0.
• Gate proven to bite: reverting F1's id_type='SCENE' in a scratch copy →
  SMOKE FAILED: unhandled TypeError in 'smoke_driver' ... DriverTarget.id expected a Object type, not Scene, exit 1.
• This PR's own blender-smoke run (which downloads real Blender on the runner) is the on-runner confirmation.

Release interaction

Per release.yml (no paths filter, patch-default), a .github/-only push to main would cut a release. This adds no shipped content and warrants no version bump, so I will squash-merge with [skip ci] (option b) so no release is cut. release.yml itself is left unchanged (separate decision).

🤖 Generated with Claude Code