[app-server][core] Add connector-level Guardian reviewer overrides

[zamoshchin-openai]

[from codex]

Summary

• add apps.<connector_id>.approvals_reviewer to override Guardian or user review routing per connected app
• apply overrides across direct app MCP calls, delegated MCP prompts, and app-server MCP elicitation review while preserving global behavior for non-app MCP servers
• expose and document the config through app-server v2 and generated schemas, while honoring global managed reviewer requirements

Validation

• just fmt
• just write-config-schema
• just write-app-server-schema
• just write-app-server-schema --experimental (validated, then regenerated standard checked-in fixtures)
• just test -p codex-config -p codex-core -p codex-app-server-protocol -p codex-app-server -E "test(app_approvals_reviewer) | test(routes_approval_to_guardian_can_use_app_reviewer_override) | test(codex_apps_mcp_uses_connector_approvals_reviewer_override) | test(delegated_mcp_guardian_abort_returns_synthetic_decline_answer) | test(config_read_includes_apps) | test(schema_fixtures) | test(write_value_supports_nested_app_paths)" (12 passed; recipe benchmark smoke passed)
• just fix -p codex-config -p codex-core -p codex-app-server-protocol -p codex-app-server

Additional validation note

• Attempted the broader affected-crate just test -p codex-config -p codex-core -p codex-app-server-protocol -p codex-app-server; it compiled the changed code but did not pass in this checkout because unrelated core integration tests could not locate target/debug/test_stdio_server and several shell/unified-exec timing tests timed out under the run.