fix(tui): use sentence case for theme mode items

[fakhriaunur]

Issue for this PR

Fixes #21191

Type of change

• Bug fix

What does this PR do?

Change "Toggle Theme Mode" to "Toggle theme mode" and similar inconsistent capitalizations in the command palette to use sentence case consistently.

How did you verify your code works?

• Visual inspection of command palette items
• No behavioral changes, only text case

Checklist

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

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found:

• PR fix(tui): use sentence case for theme mode command palette items #21192: fix(tui): use sentence case for theme mode command palette items #21192
  • Title: fix(tui): use sentence case for theme mode command palette items
  • Why it's related: This PR addresses the exact same issue (fixes Inconsistent capitalization on the two "Theme Mode" command palette items #21191) and makes nearly identical changes to use sentence case for theme mode items in the command palette. PR fix(tui): use sentence case for theme mode items #21303 (current) and PR fix(tui): use sentence case for theme mode command palette items #21192 appear to be duplicates addressing the same fix.