feat(tui): unify child tool activity views

[6iKUN6]

Problem

Closes #93.

Direct Subagent and Workflow child detail pages could still present tool calls as large native blocks instead of the compact activity projection already used by the parent Pi transcript. Read-heavy children therefore became difficult to scan, and the two child paths did not expose a consistent way to recover Pi's native evidence.

Value

Child transcripts now use the same one-line activity language as the parent for reading, searching, listing, shell, and file mutation work. Operators can scan parallel work quickly while retaining complete native call and result evidence on demand.

Approach

• Keep expansion state local to the shared AgentSessionPage and pass it through AgentTranscriptRenderer to the existing AgentToolRenderLedger.
• Delegate expanded rendering to Pi's existing ToolExecutionComponent; compact rendering continues to use the shared activity renderer rather than a child-specific formatter.
• Inherit the parent's current app.tools.expand state when a Direct Subagent or Workflow dashboard opens, while ensuring child-page toggles do not mutate the parent transcript.
• Keep the render ledger ephemeral. Persisted Workflow transcripts without a live ledger continue to use the existing bounded text fallback.
• Record the design and evidence boundary in docs/design/CHILD_TOOL_ACTIVITY.md.

Validation

• bun run check — passed on the latest upstream/main base, including config-contract, discipline, formatting, lint, and TypeScript checks.
• bun run test — passed with 1,017 Node tests, 0 failures, 1 platform skip, and 30 Vitest tests.
• Manual Pi smoke — pi list identified the local checkout as the single OpenPI source. Direct Subagent and Workflow child pages were verified for compact icon rows, Pi-native expanded evidence, collapse restoration, inherited parent state, page-local toggling, and Nerd Font rendering. This smoke preceded the final rebase; the rebase did not modify the feature runtime files, and the full automated gates passed afterward.

Impact

• User-visible behavior: Direct Subagent and Workflow child detail pages default to compact activity rows and expose the configured app.tools.expand binding in the page footer.
• Model-visible context/tools: None. Tool schemas, names, prompt metadata, results, and provider requests are unchanged.
• Runtime/lifecycle: Adds only ephemeral page-local expansion state and reuses Pi's existing renderer lifecycle.
• Persisted config/data: None. No new setting, command, transcript field, artifact, or migration.
• Compatibility/risk: Existing persisted Workflow transcripts without an in-memory render ledger retain the prior safe text fallback; native evidence remains available for live children.

[6iKUN6]

@tt-a1i Hi, PR #292 is ready for review. It implements #93, and all CI checks are passing. Thanks!

[tt-a1i]

按同步 main 后的精确 head 6d712d5 复核：新增提交仅合并已审查并已合入的 #283，#292 的 feature runtime 未产生冲突改写。Direct/Workflow child 仍共用紧凑活动 renderer，展开状态保持页面局部，模型可见内容与持久化边界不变；新 head 的 Node 22/24、Windows CI 全绿。未发现阻塞问题。