fix(track-a): promote Qt XCB GL integration repair

[blakinio]

Track A clean hosted promotion replay

Task: OTC-20260816-track-a-canonical-xcb-gl-integration-fix.
Base: trusted main@a482bba877c881d31ae903a6f8acad24debfb5c5.
Execution: GitHub-hosted, runtime_access:none.

Validated-source PR #401 proved the one-line worker repair and its regression/canonical tests: dedicated run 31959622751 passed worker syntax, XCB GL regression tests, canonical session/transition/guard/lease tests, exact official Qt 6.9.3 Git-blob fences and source invariants.

The repair removes only QT_XCB_GL_INTEGRATION=none from the canonical client launch. Official Qt 6.9.3 source shows that value clears the normal xcb_glx/xcb_egl candidate list, and the terminal physical discriminator #398 observed the exact XCB warnings emitted when no GL integration is available. QT_QUICK_BACKEND=software, exact-client identity, WARP, lease/registration/Gate-B, rollback and secret boundaries are unchanged. No replacement XCB integration/RHI/OpenGL backend or package is forced.

This branch is the clean promotion replay: same worker fix/test/evidence, without the temporary semantic validator workflow. Physical success is not claimed; it remains a separately admitted RUNTIME validation after promotion.

[blakinio]

Coordinator disposition: REJECT/SUPERSEDE — close unmerged as obsolete.

Current trusted main@d3f186414256151c9d5e03f34c5a9026b1fba500 already contains the production XCB integration repair through #402/#404: the canonical launcher has no QT_XCB_GL_INTEGRATION=none and additionally carries the later QSG_INFO=1 diagnostic. This Draft was based on that already-promoted line but still carries the older source patch that only removes QT_XCB_GL_INTEGRATION=none, so it is no longer an admissible promotion vehicle.

Subsequent current-main physical/diagnostic evidence is already terminal through #405-#413. Unique evidence from #401/#403 remains historical provenance; no unique current-main implementation change needs preservation from this PR. Do not reopen or merge #403. Any next graphics discriminator must start from current main and preserve the latest governance/runtime nonclaims.