fix(dashboard): normalize task modal timestamps to local time

[luoyanglang]

Summary

Issue: #277 - 任务详情弹窗内多个时间字段存在时区口径不一致问题
Type: Bug Fix
Severity: Medium

This PR normalizes timestamp parsing inside the task detail modal so all relevant time fields are rendered in the browser's local timezone. It removes the current UTC/local mix across scheduler info, flow log entries, and live activity timestamps.

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Root Cause

The task detail modal was using multiple incompatible display paths for the same class of timestamp values:

• edict/frontend/src/components/TaskModal.tsx:46
  • fmtActivityTime() returned ts.substring(11, 19) for string timestamps, which displayed raw UTC clock text instead of local time.
• edict/frontend/src/components/TaskModal.tsx:300
  • scheduler timestamps (lastProgressAt / lastDispatchAt) were rendered via string slicing as well.
• edict/frontend/src/components/TaskModal.tsx:363
  • flow log timestamps were also truncated directly from the ISO string.
• dashboard/server.py already emits UTC ISO timestamps via now_iso(), so the data source was mostly consistent; the inconsistency came from the frontend display logic.

// Before
flow.at            -> substring(...)
scheduler.at       -> replace('T', ' ').substring(...)
activity.at        -> substring(...)

// After
flow.at            -> shared local-time formatter
scheduler.at       -> shared local datetime formatter
activity.at        -> shared local-time formatter

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Fix Description

Changed files:

• edict/frontend/src/time.ts:1 - add a shared timestamp parser/formatter that normalizes UTC-ish strings and numeric timestamps into browser-local display values
• edict/frontend/src/components/TaskModal.tsx:4 - import the shared formatter utilities
• edict/frontend/src/components/TaskModal.tsx:46 - route activity timestamps through the shared local formatter
• edict/frontend/src/components/TaskModal.tsx:300 - render scheduler timestamps with unified local datetime formatting
• edict/frontend/src/components/TaskModal.tsx:363 - render flow log timestamps with the same local parsing logic
• edict/frontend/src/components/TaskModal.tsx:456 - align the “最后活跃” summary line with the same formatter

Why this approach:

• It keeps the fix scoped to the actual bug surface: the task detail modal.
• It avoids changing backend timestamp storage or API semantics.
• It preserves each section's existing display granularity (YYYY-MM-DD HH:mm:ss, HH:mm, HH:mm:ss) while unifying timezone handling.

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Test Results

Test	Description	Status
npm.cmd install	Install missing local frontend dependencies so TypeScript/Vite build can run in this workspace	PASS
npm.cmd run build	Type-check and production-build the frontend after the timestamp formatting change	PASS

Manual verification target:

1. Open a task detail modal.
2. Compare 最近进展 / 最近派发, flow log timestamps, 最近更新, and activity item timestamps.
3. Confirm they all now render in the same local timezone basis.

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Disprove Analysis

Is this already fixed elsewhere?

• Issue 任务详情弹窗内多个时间字段存在时区口径不一致问题，导致同一任务在不同区块出现不同时间。 #277 is still open as of 2026-04-12.
• I did not find an upstream PR referencing 任务详情弹窗内多个时间字段存在时区口径不一致问题，导致同一任务在不同区块出现不同时间。 #277.
• upstream/main still contains the string-slicing display paths in TaskModal.tsx.

Impact scope

• The change is limited to the React task detail modal.
• Backend APIs and timestamp generation remain unchanged.
• Display precision stays consistent with the existing UI intent.

Edge cases

• Numeric timestamps are normalized as seconds-or-milliseconds before formatting.
• ISO-like strings without explicit timezone suffix are treated as UTC for consistent rendering with current dashboard data.
• Invalid/empty timestamps still degrade to empty display strings instead of throwing.

Known limitation

• This PR only fixes the React task modal path served from dashboard/dist.
• It does not attempt to refactor every other historical timestamp formatter in the repo.

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Checklist

• 代码遵循现有项目风格
• 相关 issue 编号已在 PR 描述中引用（#277）
• 已提供构建验证与手动验证口径
• 未引入硬编码路径、密钥或调试输出

Found during issue triage and reproduced through code-path inspection of the current dashboard modal. Happy to adjust if you prefer a different timestamp normalization policy.