fix(core): filter unsupported media inputs

[opencode-agent]

Summary

• preserve catalog input capabilities when resolving a V2 session model
• replace unsupported outbound media with model-visible errors before provider lowering
• cover both user attachments and media nested in tool results

Fixes #38144

Checks

• bun typecheck (packages/core)
• bun test test/session-model-request.test.ts test/session-runner-model.test.ts (27 pass)
• full core suite reached 1,385 passing tests; unrelated host-only failures require a node executable and reliable process-contention timing

Requested by: @rekram1-node (Aiden Cline via Slack)

[heimoshuiyu]

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