fix(playground): report GLSL compiler errors

[devallibus]

Summary

• replace the brittle gl.CURRENT_PROGRAM check in the playground with Three's renderer.debug.onShaderError hook
• collect and normalize GLSL compile/link diagnostics into a small reusable helper
• add regression coverage for shader diagnostic extraction and wire it into test:web

Verification

• bun run test
• bun run build:web
• manual local repro against the playground API + browser-connected session confirms invalid GLSL now returns non-empty compilationErrors

Closes #68.

[devallibus]

LGTM. The switch from gl.CURRENT_PROGRAM to renderer.debug.onShaderError is the right call — hooks into Three.js's own error reporting instead of relying on brittle WebGL state queries. The diagnostic extraction helper is clean, well-tested, and properly handles edge cases (dedup, fallback chain, both throw and non-throw paths).

Two minor nits left as inline comments (redundant | null type, optional missing test for link-only fallback). Neither blocks merge.

[devallibus]

unknown | null is redundant since unknown already includes null. Stylistically fine — communicates intent — but worth knowing it's a no-op at the type level.

Suggested change

	vertexShader?: unknown | null
	fragmentShader?: unknown | null
	vertexShader?: unknown
	fragmentShader?: unknown

[devallibus]

Nice fallback chain. One path that isn't covered by tests: if onShaderError fires but neither shader reports a compile failure and getProgramInfoLog returns empty, this line is reached. Easy to add:

runTest('collectShaderDiagnostics falls back to a generic link message', () => {
  const diagnostics = collectShaderDiagnostics({
    gl: mockGl,
    program: { log: null },
    vertexShader: { ok: true, log: null },
    fragmentShader: { ok: true, log: null },
  })
  assert.deepEqual(diagnostics, [
    { kind: 'glsl-link', message: 'GLSL program linking failed.' },
  ])
})

nit / optional

[devallibus]

Good use of renderer.debug.onShaderError — this is the official Three.js hook and much more reliable than querying gl.CURRENT_PROGRAM after the fact. The try/catch/finally ensures the hook is always restored, and the post-render shaderDiagnostics.length > 0 check correctly handles the case where Three.js calls onShaderError without throwing (it may continue with a fallback shader). Well done.