feat(tui): show per-part timestamps for thinking and tool blocks - #42499

Issue for this PR

Closes #42498

Type of change

• New feature

What does this PR do?

When the existing /timestamps toggle (session.toggle.timestamps) is enabled, each message part now renders its own start timestamp alongside the message-level timestamp:

• Thinking header: Thought: plan migration · 2.3s · 3:41 PM
• Inline tool row (e.g. $ npm run build, reads, greps): appends · 3:41 PM next to the tool label, in both pending and completed states
• Tool block header (shell output, tool output blocks): # Running in packages/tui · 3:41 PM

Parts already carry time.start in the protocol, so this is a pure TUI rendering change. The time uses the existing Locale.todayTimeOrDateTime helper (matches the message-level format: time for today, date+time otherwise).

How did you verify your code works?

• bun typecheck in packages/tui (plus full monorepo turbo typecheck via pre-push hook)
• bun test in packages/tui: 193 pass, 1 skip, 0 fail (incl. the 17 inline-tool-wrap-snapshot tests that render InlineToolRow standalone — the new time prop is optional and theme-free)

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR