fix(ai): admit capability-bound Codex sessions

[first-assist]

Outcome

Admits exact AiProviderCapabilitySessionBinding values on an immutable Codex app-server registration so capability-bound retained descriptors can create, resume, discard, and clean up threads. Bare final fingerprints remain impossible to admit.

Security boundary

• validates EagerExact, ProviderDeferred, or FixedBroker mode, model, reasoning effort, and embedded raw executable/sandbox registration identity
• rejects ClientDeferred because later definition installation cannot be frozen into one Codex thread
• keeps the raw registration identity unchanged to avoid a circular fingerprint
• clears admitted bindings after any later identity-bearing registration change
• preserves rejection for unadmitted capability fingerprints

Verification

• graphql-orm-ai 0.88.2 release-policy gate
• cargo-semver-checks against 4036cba
• 317 library tests passed, 2 live Codex tests ignored, 0 failed
• focused capability-bound create/resume/discard and EagerExact admission tests passed
• warnings-denied Clippy and Rustdoc
• SQLite, PostgreSQL, and MSSQL compile lanes
• workspace inventory, documentation validation, and git diff --check

Documentation impact

• Documentation updated
• No documentation impact

README, provider-session guide, changelog, migration guide, and generated workspace inventory document the exact capability-session admission. No schema or data migration.

[first-assist]

Refreshing the pull_request event payload after adding the required documentation-impact checkbox; no code or reviewed tree change.