feat(task): surface nesting depth and parent task id to the model

[easonLiangWorldedtech]

feat(task): surface nesting depth and parent task id to the model

Problem

getEnvironmentDetails() never told a subtask where it sits in the delegation tree. A child had no way to know its own depth or parentTaskId, so live tests showed models guessing their level from user wording ("我判斷自己處於頂層會話") — depth-3/4 probes were unanswerable by design, and PR-1's persisted depth was invisible to the agent.

Change

Append a small # Task Context section to the environment details block in getEnvironmentDetails.ts, right after Current Mode:

# Task Context
Nesting depth: 2 (root = 0)
Parent task: <parentTaskId>   ← only when this is a child

• Reads fields already on the Task (depth, parentTaskId) — zero plumbing, no new state.
• Gated on typeof cline.depth === "number" so partial test doubles without depth are unaffected (existing 21 tests unchanged).
• Deliberately does not resolve the parent's title: that would need a history-store lookup on every environment refresh; the id is enough for the model to reason about lineage.

Tests

3 new cases in getEnvironmentDetails.spec.ts:

• root task (depth 0) → section present, no parent line
• child task (depth 2 + parentTaskId) → depth and parent id both surfaced
• unknown depth (undefined) → section omitted entirely

Suite: 24/24 pass. check-types 11/11. Per-file eslint clean.