feat: add Taskmarket action provider (on-chain bounty marketplace integration)

[YfengJ]

Description

This PR adds a new Taskmarket action provider, integrating Taskmarket — an on-chain bounty marketplace where agents complete digital work for escrowed USDC rewards — into AgentKit.

With this provider, an AgentKit agent gains a full delegation loop: it can recognize that a request is better delegated to external workers, discover escrow-backed bounties, inspect a precise task before acting, and (with explicit user authorization) post new work or deliver completed work:

• list_tasks — browse open tasks with status/limit/reward/tag filters
• get_task — fetch one task's full record (reward, expiry, escrow tx, submission window)
• my_submissions — track the wallet's submissions and their award state
• submit_work — submit a deliverable file (requires confirm: true)
• create_task — create a task and escrow its USDC reward (requires confirm: true)

Design notes:

• The provider delegates to the official taskmarket CLI (npm install -g @lucid-agents/taskmarket), so signing and payment stay inside the CLI's keystore — the provider never reads or exports wallet keys.
• Both spend-capable actions are gated behind an explicit confirm input, so no funds move without user authorization; the three discovery/tracking actions are read-only.
• No existing Taskmarket integration exists in this repository (searched taskmarket across the repo — zero matches before this PR).

Closes nothing (new feature, no tracking issue).

Tests

Unit tests added in taskmarketActionProvider.test.ts covering:

• CLI argument construction for all five actions (filters passed through correctly)
• CLI error surfacing (stderr detail included in returned message)
• Both confirm gates: submit_work and create_task refuse to invoke the CLI and clearly state the consequence when confirm is not true

Manual check of the delegation flow against the live marketplace:

Setup: taskmarket CLI installed and initialized (taskmarket init), wallet registered on Base

Prompt: list open Taskmarket tasks with a reward of at least 2 USDC

<agent output>
{"ok":true,"data":{"tasks":[...7 open tasks with ids, rewards, expiries, submission counts...]}}
</agent output>

Prompt: get_task 0x7f06ef6d25e5768d2d96dd4f49230542b1d175e994d0eaa421627b72031c9f71

<agent output>
{"ok":true,"data":{"id":"0x7f06ef...","reward":"2000000","escrowTxHash":"0x93dd868b...","expiryTime":"2026-08-23T00:15:04.189Z","stakeRequired":false,"submissionWindowOpen":true,...}}
</agent output>

my_submissions similarly returned the wallet's live submission list via taskmarket task my-submissions.

Checklist

• Added documentation to all relevant README.md files
• Added a changelog entry

[cb-heimdall]

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