feat: Format token counts with locale-aware thousands separators

[dev-miro26]

Related Issue

Closes #1434

Description

The token count displayed in the bottom-left of the app (and in the history sidebar) can be hard to read when large numbers are involved (e.g. 19994406).

This PR adds locale-aware thousands separators to all token count displays by using Number.toLocaleString(), so the value renders as 19,994,406 (en-US), 19.994.406 (de-DE), etc., depending on the user's regional settings.

Files changed:

• src/components/ChatBox/HeaderBox/index.tsx: Chat header token count
• src/components/HistorySidebar/index.tsx: Active and history project token counts and update stylelint

Note: GroupedHistoryView components already used .toLocaleString() — no changes needed there.

Testing Evidence (REQUIRED)

eigent-issue1434.mp4

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

[dev-miro26]

Hi, @4pmtong @Wendong-Fan
Could you review my first PR? Please left your feedback kindly.
Thanks

[dev-miro26]

Hi @4pmtong
I am sorry, I know you are so busy. If you don't mind I hope you review this my first PR and leave the feedback kindly.
Thank you.

[dev-miro26]

Hi, @bytecii
Could you review this PR too?

[dev-miro26]

Hi @4pmtong
Could you please review this PR too?