fix: harden storage semantics (backport #4118)

[mergify]

Fixes issues in the storage system by guaranteeing immediate durability for responses and ensuring background writers stay alive. Three related fixes:

• Responses to the OpenAI-compatible API now write directly to Postgres/SQLite inside the request instead of detouring through an async queue that might never drain; this restores the expected read-after-write behavior and removes the "response not found" races reported by users.

• The access-control shim was stamping owner_principal/access_attributes as SQL NULL, which Postgres interprets as non-public rows; fixing it to use the empty-string/JSON-null pattern means conversations and responses stored without an authenticated user stay queryable (matching SQLite).

• The inference-store queue remains for batching, but its worker tasks now start lazily on the live event loop so server startup doesn't cancel them—writes keep flowing even when the stack is launched via llama stack run.

Closes #4115

Test Plan

Added a matrix entry to test our "base" suite against Postgres as the store.

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This is an automatic backport of pull request #4118 done by Mergify.

[mergify]

Cherry-pick of 492f79c has failed:

On branch mergify/bp/release-0.3.x/pr-4118
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Changes to be committed:
	modified:   .github/actions/setup-test-environment/action.yml
	modified:   llama_stack/providers/utils/sqlstore/authorized_sqlstore.py
	modified:   tests/integration/fixtures/common.py
	modified:   tests/integration/suites.py

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   .github/workflows/integration-tests.yml
	added by them:   llama_stack/distributions/ci-tests/run-with-postgres-store.yaml
	both modified:   llama_stack/distributions/starter-gpu/run.yaml
	both modified:   llama_stack/distributions/starter/run.yaml
	both modified:   llama_stack/distributions/starter/starter.py
	both modified:   llama_stack/providers/utils/inference/inference_store.py
	both modified:   llama_stack/providers/utils/responses/responses_store.py
	deleted by us:   tests/integration/ci_matrix.json

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally