feat(agentkit): add Taskmarket action provider

[rajishere9]

Summary

• add a Base-only TaskMarketActionProvider for discovering open Taskmarket USDC work
• add read-only task listing/detail actions and a signed text-artifact submission action
• use Taskmarket's canonical presigned-upload flow, artifact-key binding signature, and idempotency key
• require an explicit confirmation field for the public, irreversible submission action
• never perform automatic X402 payments; payment-required responses are returned without retrying
• validate task IDs, artifact filenames, MIME types, size, HTTPS upload URLs, and supported network
• add colocated documentation, unit tests, and a changeset

Verification

• tsc --noEmit
• focused Jest suite: 7 passing tests
• ESLint for the changed provider and exports
• Prettier check
• git diff --check

The provider uses the connected EVM wallet only for the documented Taskmarket signatures. It does not upload credentials or private data, and it never signs arbitrary transactions.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2