[Story]: Enforce content exclusion in lightbridge-code-intelligence indexing

## Summary
Coordinate with lightbridge-code-intelligence to enforce content-exclusion rules in its indexing pipeline, so excluded repos/paths are never indexed or surfaced in suggestions.

## Intent / Source of truth
lightbridge-code-intelligence owns indexing; this control is worthless without real enforcement there. Part of [Epic] Content and path exclusion controls.

## Scope
- [ ] Cross-repo integration point: lightbridge-code-intelligence reads exclusion rules from lightbridge-authz before/during indexing
- [ ] Enforcement covers both initial indexing and incremental re-index
- [ ] Cross-repo integration test proving an excluded path never appears in an index or a suggestion

## Out of scope
- Redesigning lightbridge-code-intelligence's indexing architecture beyond the exclusion check

## Verification
An end-to-end test: mark a path excluded, trigger indexing, confirm the path is absent from the index and never surfaced in a suggestion.

## Risk assessment
This is a cross-repo dependency — file the corresponding coordination issue in lightbridge-code-intelligence and track it explicitly; a config-only implementation with no real enforcement would be a false compliance claim to customers.

## AI Usage Declaration
Drafted with AI assistance during the 2026-08-13 cross-repo backlog consolidation and enterprise-readiness research. A human owns intent, verification and consequences.