feat: lint GLSL in JS/TS tagged template literals

[johncarmack1984]

Lint GLSL written inline in JS/TS glsl`...` tagged template literals — and the /* glsl */ `...` marker form — the way deck.gl/luma.gl projects keep shaders next to their new Model(...) call rather than in separate .glsl files. The most-requested capability in this space.

What's covered

• Extraction (src/embed.rs, new): a heuristic scanner — sibling to derive.rs — that finds each tagged-template shader in .ts/.tsx/.js/.jsx/.mts/.cts/.mjs/.cjs, tracking strings/comments so a backtick in a "..." string or glsl inside a longer identifier isn't mistaken for a shader. It records a per-line map back to the host file.
• CLI: glslint check 'src/**/*.ts' validates each embedded shader and maps every diagnostic — glslang errors and the source lints — to the exact host .ts line and column (embed's per-line host map composed with the assembler's own line map).
• LSP: the server diagnoses JS/TS documents live (the VS Code extension now activates on and selects them). The GLSL-only features — hover, definition, completion, outline — stay on .glsl files.

Practical cases

• Interpolations (${...}): a template with any interpolation is an incomplete translation unit (the injected value can declare symbols the shader uses, or use ones it declares), so it's checked with the source-level lints only — never a validation error that might be our own substitution's fault — and gets one informational note. Non-interpolated templates are fully validated. The ${...} is blanked to spaces (newlines preserved) purely so the lints' line/column math stays exact.
• Multiple templates per file, handled independently.
• Stage inference: a stage-specific builtin decides it (gl_Position/gl_VertexID → vertex, gl_FragCoord/discard → fragment, local_size_x → compute), then the binding name, then a fragment default — ordered so the default and name hint are only reached when no stage-specific builtin is present, and therefore can't cause a wrong-stage false positive. No main → a chunk wrapped syntax-only under its inferred stage.
• luma module injection when a new Model({ modules }) call wires up the shader's binding, via the new derive_for_binding.

The glslang backend is untouched. New Severity::Note (→ LSP INFORMATION). Fixtures + unit/integration tests cover extraction, mapping accuracy, the interpolation path, and the stage-guess false-positive regression.

Docs: README gains a "Shaders inside JS/TS" section and an embed.rs entry in "How it works"; the extension README documents the JS/TS support.