fix: v2/v3 backwards compat for create_media_buy, update_media_buy, get_products

[EmmaLouise2018]

Summary

• Strip legacy brand_manifest before strict Zod validation fires for create_media_buy and update_media_buy — v2.5 callers no longer hit "Request validation failed: Unrecognized key: brand_manifest"
• Convert brand (BrandReference) → brand_manifest bare domain URL when adapting requests for v2 servers — previously brand passed through and v2 servers rejected it
• Throw a clear error when proposal_id is sent to a v2 server (proposal mode is v3-only; v2 requires explicit packages)
• Strip catalog from package items for v2 servers (optimization_goals was already stripped; catalog was missed)
• Fix dead-code delete: account_id → account in adaptGetProductsRequestForV2
• Align brand URL format: get_products and create_media_buy both now use https://<domain> (bare domain) consistently

Test plan

• New tests in request-validation.test.js: brand_manifest stripped pre-validation for create_media_buy, brand wins when both supplied, mock-based test verifying conversion at the transport layer
• Updated + new tests in v3-compatibility.test.js: brand → brand_manifest conversion, brand-with-no-domain preserved, proposal_id throws, catalog stripped from packages, adaptUpdateMediaBuyRequestForV2 brand passthrough documented
• All existing tests pass
• Build and typecheck clean

[nastassiafulconis]

Overall approach is solid — lifting brand_manifest normalization to cover more task types and the new v2 adaptation for brand/catalog/proposal_id all make sense. A couple things to fix up before this is good to go though.

[EmmaLouise2018]

Addressed all 5 review comments — pushed the fixes:

#1 (creative-adapter.ts:97) — brand?.domain guard
Changed brand ? \https://${brand.domain}`→brand?.domain ? `https://${brand.domain}`so a brand object without adomainfield doesn't produce"https://undefined"`.

#2 (creative-adapter.ts:98) — preserve brand when no domain
When brand is present but has no domain (so can't be converted to a brand_manifest URL), brand is now re-added to the return value — consistent with adaptGetProductsRequestForV2 which also leaves brand on the object when it can't be converted. Added a test for this case.

#3 (SingleAgentClient.ts:2032) — remove update_media_buy from normalization block
Dropped update_media_buy from the brand_manifest → brand normalization condition. Neither the v2 nor v3 update_media_buy schemas have a brand field, so the normalization was wrong to include it. Added a comment to the condition explaining the deliberate exclusion.

#4 (request-validation.test.js:130) — verify actual conversion, not just no-throw
Added a new test that mocks A2AClient.fromCardUrl to capture the parameters actually sent to the server. It asserts that brand_manifest is not forwarded as an object (i.e., normalization happened). The existing no-throw tests are kept for the validation-layer coverage.

#5 (v3-compatibility.test.js:349) — adaptUpdateMediaBuyRequestForV2 brand tests
Added a test that verifies the adapter passes brand through unchanged and doesn't produce a brand_manifest field — documenting the "no conversion" contract since neither schema has that field.

[nastassiafulconis]

All 5 comments addressed in ca7fc3b. Looks good to merge.