fix(adagents): scope PR to function add only; revert schema-pin bump

The 3.1.0-beta.2 bundle introduces spec drift well beyond this PR's
scope — `cache_scope` becomes required on product responses, new
`sponsored-intelligence` specialism + `search_brands` webhook task type,
new `validate_input_brand_claims` endpoint. Each of those needs its own
focused change (constant updates, fixture refreshes, capability surface
work); bundling them with the AAO inverse-lookup function would block
landing both.

This commit:
- Reverts ADCP_VERSION to 3.0.7 (the prior pin).
- Drops `schemas/cache/3.1.0-beta.2/` from the tree; the new
  `fetch_agent_authorizations_from_directory` works with hand-written
  Pydantic models and does not need the v3.1 bundle on disk.
- Regenerates `tests/fixtures/public_api_snapshot.json` to record the
  intentional new public exports (function + result types).

The v3.1 schema-pin bump (and the codegen `../`-resolution fix noted in
the PR body) move to a separate PR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bokelley