feat: add strict SmolVM WebGL probe groundwork

[Qubitium]

Summary

• add a strict 2560×1440 public Three.js WebGL terrain probe, with a real-canvas and non-software-renderer gate
• add CDP GPU/page-error telemetry and keep the ZPU Mosaic executor constrained to CPUs 0,1
• add ANGLE's packed WebGL color renderbuffer format family as optimal-tiled, blendable attachment-only surfaces
• document the current Tier B boundary accurately

Verification

• tools/limited-cpus.sh zig test src/vulkan/driver.zig -lc — 373/373 passed
• staged the ReleaseSafe ICD in SmolVM and ran tools/smolvm-chrome.sh webgl at 2560×1440

Current boundary

The live probe deliberately fails: Chromium is confirmed as ANGLE ... Vulkan ... ZPU Experimental CPU, but no WebGL context is created because D24/S8 and multisample attachment semantics are not implemented. This PR does not claim a WebGL or FPS result.

Performance target

The target is a sustained 60 FPS at 2560×1440, verified by the same live-canvas telemetry with a 17 ms rAF p99. No higher FPS target is claimed.