[Bugfix] Reconcile env-var inventory with post-#6217 main drift

[hsliuustc0106]

Problem

Main is red after the merge of #6217 (build 14119, Simple · Other Test lane): both new environment-variable ratchet tests fail.

FAILED tests/config/test_environment_variables.py::test_statically_resolvable_environment_accesses_are_classified
  Extra items in the left set: 'VLLM_OMNI_ASYNC_OUTPUT_TIMEOUT'
FAILED tests/config/test_environment_variables.py::test_model_and_benchmark_inventory_entries_are_still_referenced
  Extra items in the left set: 'ROSVOT_SOURCE_DIR'

This is merge-window drift, not a defect in #6217 itself — its CI ran before two sibling commits landed:

• [Bugfix] Make the async-output wait bound configurable and default it higher #6255 added the VLLM_OMNI_ASYNC_OUTPUT_TIMEOUT read in vllm_omni/diffusion/diffusion_engine.py (async-output wait bound) — an unclassified static access.
• [CI]Remove SoulX-Singer support #6362 (SoulX-Singer removal) deleted the last package reference to ROSVOT_SOURCE_DIR, leaving a dead inventory row.

Fix

• Classify VLLM_OMNI_ASYNC_OUTPUT_TIMEOUT as PUBLIC_OMNI and document it in the Serving and runtime table of the reference page (float seconds, default 600, non-float/<=0 warns once and falls back — matching the engine's resolution-on-request-path contract).
• Drop the stale ROSVOT_SOURCE_DIR model-specific row (disposition deprecate_remove is now moot: the implementation is gone).
• Update the pinned snapshot counts (PUBLIC_OMNI 22→23, MODEL_SPECIFIC 57→56, DEPRECATE_REMOVE 7→6) in the test and the audit-count prose/table in the reference page.

Validation

No runnable env on the review host, so the AST ratchets were validated standalone by loading the inventory module directly and exec'ing the test module:

• before: exactly the two CI failures reproduce;
• after: all inventory/scanner/docs ratchets pass (test_inventory_matches_reviewed_snapshot_counts, prefix rule, classified-accesses, still-referenced, scanner coverage, reference page, redaction). The two collect_env tests were not runnable locally (need vllm import); they are untouched by this change — collect_env derives its safe-report set from the inventory, and a numeric timeout knob is not sensitive.

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[vllm-omni-review-bot]

This PR was classified as CI work.

CI owner: @yenuo26

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