Expose blessed workspace capabilities as an optional Agents API executor

[chubes4]

Problem

Data Machine Code owns concrete workspace and Git side effects: workspace registry, worktree lifecycle, file operations, GitHub operations, and code-task scaffolding. Those should not be imported into Studio Web directly.

Once Agents API owns generic task execution plumbing, DMC should expose blessed workspace capabilities as an optional executor/tool provider while keeping all filesystem and Git side effects inside DMC.

Upstream tracker: Automattic/agents-api#309

Scope

Add an optional Agents API adapter that registers DMC capabilities only when Agents API executor plumbing is present.

Potential target:

• data-machine-code/blessed-workspace

Capabilities may include:

• filesystem.read
• filesystem.write
• git.diff
• git.commit
• github.pr

Required code areas

• data-machine-code.php
• inc/Abilities/WorkspaceAbilities.php
• inc/Abilities/CodeTaskAbilities.php
• inc/Tools/AbilityToolProjections.php
• inc/CodeTask/CodeTaskCreator.php
• New adapter namespace, for example inc/AgentsApi/WorkspaceExecutorAdapter.php

Non-goals

• Do not make Studio Web call DMC directly.
• Do not move workspace/worktree/Git side effects into Agents API.
• Do not require DMC for Codebox or Studio Web to function.

Acceptance criteria

• DMC registers executor/tool capabilities only when the Agents API executor substrate exists.
• Registered capability metadata is generic and side-effect boundaries are explicit.
• Workspace side effects still go through DMC-owned abilities/services.
• Tests prove the adapter is optional and does not alter existing DMC ability/tool behavior when Agents API executor plumbing is absent.