Move login into Account tab and rename settings tabs

[sejas]

Related issues

• Fixes STU-1423

Proposed Changes

• Merged the Account tab (login/logout) into the Usage tab, creating a single "Account" tab that shows auth state plus usage info (snapshots, AI prompts)
• Renamed "Preferences" tab to "General" and updated internal tab key from preferences to general
• Renamed "Usage" tab to "Account" and updated internal tab key from usage to account
• Added a "Skills" tab (placeholder) behind the enableAgentSuite feature flag
• Renamed usage-tab.tsx to account-tab.tsx and old account-tab.tsx to user-info.tsx to match new tab names
• UsageTab (now AccountTab) uses useAuth() hook directly instead of receiving auth props from parent
• Memoized tabs array to prevent unnecessary re-renders
• Added bottom padding to tab content container
• Updated e2e page objects and unit tests

Testing Instructions

1. Start the app with npm start
2. Open Settings (gear icon or Cmd+,)
3. Verify tabs show as "General" and "Account"
4. On the General tab, verify language, editor, terminal, CLI toggle are present
5. On the Account tab:
   • When logged out: verify "Log in" button is shown
   • When logged in: verify user info, preview sites, and AI assistant sections are shown
6. Enable enableAgentSuite feature flag and verify "Skills" tab appears between General and Account

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors? (Tests pass, no errors)

[wpmobilebot]

📊 Performance Test Results

Comparing 31061aa vs trunk

app-size

Metric	trunk	31061aa	Diff	Change
App Size (Mac)	1236.60 MB	1236.60 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	31061aa	Diff	Change
load	1895 ms	1897 ms	+2 ms	⚪ 0.0%

site-startup

Metric	trunk	31061aa	Diff	Change
siteCreation	7104 ms	7083 ms	21 ms	⚪ 0.0%
siteStartup	3927 ms	3915 ms	12 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[katinthehatsite]

I am not sure we need the comments here, it seems self-explanatory to me

[katinthehatsite]

I had one minor comment but the changes look good to me otherwoise and work as expected:

I will merge this PR so that we can move ahead with STU-1405 to avoid causing conflicts.