Keep Wiki data out of runtime images and clarify search semantics

[areshand]

Why

The runtime build context currently copies the checked-in repository catalog into every agent image. The production trace also treated lexical search/name frequency as repository usage, which the Wiki cannot support.

What changes

• Exclude wiki-service/catalog from the runtime image build context while retaining the provider-neutral wiki-query client.
• Make query responses explicitly state scoreMeaning: "lexical-relevance-only" and supportsAggregation: false.
• Require agents to report insufficient evidence for usage/popularity/dependency aggregates unless a cited Wiki page or authoritative external read provides them.
• Document and test both contracts.

Validation

• Wiki service tests — 25 passed
• Runtime container contract tests — 5 passed

Deployment

Source-only PR. It does not alter the S3 Wiki corpus, sync data, or deploy a service.