docs(gsplat): drop "unified" framing now that it's the default

[mvaligursky]

Follow-up cleanup to the unified-default flip (#8802, #8803, #8804). Unified rendering is now the default and the unified property is @deprecated + @ignore, so the public API docs and examples shouldn't be framed around "unified mode" any more — it's just gsplat rendering.

Changes (engine source):

• GSplatComponent:
  • Remove the ## Unified Rendering section from the class JSDoc.
  • Strip the JSDoc blocks from material get/set and highQualitySH get/set (both are legacy-only and only documented the unified/non-unified distinction).
  • Drop "unified" qualifiers from workBufferUpdate, workBufferModifier, setParameter, and getInstanceTexture JSDocs.
• GSplatComponentSystem: drop "in unified mode" from the material:created and frame:ready event JSDocs, and from getMaterial JSDoc.
• GSplatParams: class JSDoc "Parameters for GSplat unified system" → "Parameters for the GSplat system"; drop "unified" qualifier from dataFormat, material, and format JSDocs.
• GSplatContainer: drop "non-unified rendering" from the class example comment, drop unified: true from the addComponent example, drop "unified" qualifier from the centers JSDoc.

Changes (examples — gaussian-splatting/ folder, 29 files):

• Remove unified: true from every addComponent('gsplat', { ... }) call (~40 occurrences) — it's the default now and the property is deprecated.
• Reword/remove comments that frame things around "unified" (e.g. // Create hotel gsplat with unified set to true → // Create hotel gsplat).
• Drop three stale orbit-pivot comments ("unified gsplats have no mesh AABB for focusEntity framing") — these became factually incorrect once fix(gsplat): unified-mode follow-ups (orbit-camera AABB, internal warnings) #8803 made orbit-camera.js unified-aware.
• Update global-sorting example header from "demonstrates unified gsplat rendering" to "demonstrates global gsplat sorting" — what the example actually shows.

API Changes:

• None. All edits are docs/comments/examples. No runtime behaviour or public-API surface changes.

Notes:

• Remaining unified mentions in the engine are all either internal (private fields, code comments, code branches), runtime warning strings (which must keep the property name so users can search for it), @ignore'd JSDoc, or directory names — none render in public docs.
• The legacy gsplat.unified = false opt-in still works and still emits the one-time Debug.deprecated warning from [BREAKING] Deprecate GSplatComponent#unified and default it to true #8802. This PR doesn't remove the legacy mode itself.