feat: show persistent delegated tasks in Codex Desktop

[SanAntonio021]

Summary

• Set threadSource: "user" for newly created persistent task and rescue
  threads so Codex Desktop includes them in its task list.
• Preserve the existing handling of reviews, transfers, and stop-gate runs.
• Add runtime tests for thread-source selection.

Problem

Persistent task and rescue threads already support resume by thread ID.
Codex Desktop lists user threads, while the plugin currently leaves the source
value unset for these runs. Users therefore need the thread ID to reopen the
conversation in Desktop.

Approach

buildThreadParams() now accepts an optional threadSource. New persistent
task and rescue threads use "user". Review, adversarial review, transfer,
and stop-gate paths keep their existing source handling.

The origin metadata still identifies Claude Code as the caller.

Flow	Result
New persistent task or rescue	Listed in Codex Desktop
Resume an existing task	Reuses the same thread
Review or adversarial review	Existing behavior preserved
Transfer	Existing behavior preserved
Stop-gate review	Existing behavior preserved

User impact

A delegated task appears in the Codex Desktop sidebar. The user can open it,
continue the conversation in Desktop, and later resume the same thread from
Claude Code. Creating the thread leaves the current Desktop task in focus.

Validation

• Focused thread-source tests: 4/4 passed.
• Version metadata, plugin manifest validation, and syntax checks passed.
• App-server type generation and TypeScript compilation passed on Windows 11.
• A Windows 11 canary confirmed automatic sidebar listing, stable task focus,
  one shared thread ID, and history continuity between Desktop and Claude Code.
• The thread remained available after the Claude Code session ended.
• Full-suite comparison: 86/91 passed on both the feature implementation and
  the upstream baseline, with matching results across all 91 tests.