Add enterprise docs structure and include pending core maintenance updates.

docs/features/query-and-indexing.md

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+# Query And Indexing
+
+## Purpose And Business Outcome
+
+Deliver predictable query correctness and performance using expression translation with index-aware execution.
+
+## Scope And Non-Goals
+
+Scope:
+- LINQ query translation
+- Primary and secondary index usage
+- Scan fallback where index optimization is not applicable
+
+Non-goals:
+- Full SQL compatibility
+- Distributed query federation
+
+## User And System Workflows
+
+1. Consumer submits LINQ expression.
+2. Query planner evaluates index opportunities.
+3. Engine executes index-backed or scan path.
+4. Results are materialized to consumer entities.
+
+## Interfaces And APIs
+
+- `AsQueryable()` and query provider components
+- `CollectionIndexManager`
+- Index implementations under `src/CBDD.Core/Indexing`
+
+## Permissions And Data Handling
+
+- Query access follows host application authorization policy.
+- Indexed data inherits the same sensitivity classification as source payloads.
+
+## Dependencies And Failure Modes
+
+Dependencies:
+- Valid index metadata and storage consistency
+- Expression visitor correctness
+
+Failure modes:
+- Incorrect predicate translation
+- Missing/ineffective indexes
+- Performance regressions due to scan-heavy paths
+
+## Monitoring, Alerts, And Troubleshooting
+
+- Track query-related regressions in automated tests.
+- Use [`../runbook.md`](../runbook.md) for incident handling.
+- Follow [`../security.md`](../security.md) for sensitive data and access constraints.
+- Use [`../troubleshooting.md`](../troubleshooting.md#query-and-index-issues) for remediation.
+
+## Rollout And Change Considerations
+
+- Query planner/index behavior changes require benchmark comparison and regression coverage.
+- Document breaking semantics in release notes.
+
+## Validation Guidance
+
+- Run query, index, and optimizer test suites in `tests/CBDD.Tests`.
+- Confirm coverage gate with `bash scripts/coverage-check.sh`.