CCC Non-Agent `match_all` Convenience API
## Problem/motivation
Follow-up to:
#3586202
_**Verify this is still an issue and the solution approach before proceeding**_
_**Assess if this should be pre-RC1 or post-1.0 and move for the latter**_
`AiContextRequestFactory::fromParameters()` defaults to `match_all` when there
is no agent ID and no explicit selection mode. The convenience APIs document
that empty scopes match all published context.
This is useful for preview/tooling, but frequent non-agent callers can
accidentally trigger full-catalog scans.
Treat this as RC1 work if these APIs are expected to be common integration
points in 1.0.
## Solution
Recommended options:
- Keep `match_all` but document it as an intentionally broad mode.
- Require explicit `selection_mode=match_all` for broad non-agent calls.
- Apply stricter default item/token caps for convenience methods.
- Log or expose diagnostics when a broad match scans many candidates.
## Tasks
- Check against other issues to make sure it wasn't separately reported
- Verify this is still an issue before proceeding
- Verify the solution approach before proceeding
- Update code
- Review and test
## AI usage disclosures
- [x] AI Assisted Issue
- [ ] AI Assisted Code
- [ ] AI Generated Code
issue