v0.2.0: splats, copy/paste, faster homes, seat facing, and a full bug sweep

Frame Studio
- Gaussian splats (PLY, SPZ v2-v4), PLY vertex colours, panorama skies
- Copy, cut, paste and duplicate for objects, splats and world items
- Walkable-area rebake moved off the UI thread; viewport one frame sooner;
  refresh-locked pacing (FS_PACE=timer for the old one)
- Fixed: bundle thumbnail use-after-free crash, auto-save deleting
  environments, saves into scratch copies, edits lost on non-ASCII paths,
  unopenable manifests with inf/nan, bundle save data loss, opening a home
  marking it changed, gizmo NaN, long paths, many malformed-file crashes
- Updater verifies sha256, journals the swap and never leaves the exe missing

Frame Home
- Seats turn you to face their way
- Draw batching (Hand Tutorials up to ~20% less GPU time), cut-out EQUAL pass,
  late head-pose read before submit
- Proper queue-family hand-over to the compositor layer; layer descriptor
  generations and seqlocked slots; structural SPIR-V check
- Fixed: hangs/crashes on damaged .fenv files and shaders, render-pass
  validation error, sync hazard in the foveation smoothing pass, unverified
  update downloads, half-done installs

Tests: tests_loco/env_share/spv_check wired into CMake (FRAME_TESTS) and CI.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VsaXGU27gsrXjDoFtyFJP9

docs/studio-guide.md

@@ -111,7 +111,7 @@ edges, grey are floors you can't reach. **W** shows or hides it.
 | Item | What it does on the headset |
 |---|---|
 | **Spawn Point** | where you start, facing the way it faces |
-| **Seat** | a place to sit: point at it and pull the trigger; its "stand up here" ring is where you get up |
+| **Seat** | a place to sit: point at it and pull the trigger; you sit facing the way its arrow points; its "stand up here" ring is where you get up |
 | **Teleport Hotspot** | a spot the teleport arc snaps to |
 | **Surface** | a box you can scale into a floor, a step or a wall |
 | **Invisible Wall** | stops you; never drawn on the headset. Scale and turn it to fit; where it stands is no longer walkable |