feat: add Taskmarket action provider

[tiburzy-dev]

Summary

• add a Taskmarket action provider for public task discovery and task detail reads
• add an explicitly confirmed task-creation action that pays USDC escrow through x402 on Base mainnet
• enforce a configurable per-call reward limit and a confirm=false dry-run before any paid request
• document the provider and add a patch changeset

The read actions work with any AgentKit wallet network. Task creation is limited to an EVM wallet on Base mainnet and does not send a request unless confirm=true is supplied after the exact specification and reward have been reviewed.

Validation

• pnpm --filter @coinbase/agentkit check
• pnpm --filter @coinbase/agentkit lint
• pnpm --filter @coinbase/agentkit format:check
• pnpm --filter @coinbase/agentkit build
• targeted Taskmarket tests: 6/6
• full AgentKit Jest suite: 61 suites, 870 tests
• live read-only Taskmarket list/detail smoke test
• dry-run and reward-limit guard smoke tests; no paid request sent

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2 Emergency override progress: 0/5 These approvals do not satisfy normal or CODEOWNER requirements because the commit identity is unverified.	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