fix(desktop): polish list pages — Usage, Memory, and Web Search

[Astro-Han]

Sub-issue of #1303. Visual/layout audit of the list/long-content pages:

• Usage — usage-settings-page.tsx — story Usage
• Memory — memory-settings-page.tsx — story Memory
• Web Search — web-search-settings-page.tsx — story WebSearch

Shared themes: DataTable overflow, Empty states, long text and Chip lists. Story variants for empty vs. populated and long-content states are expected deliverables. Scope and acceptance criteria: see #1303.

Known remaining work

#1479 must not close this issue until its final result is verified together with the shared wrapper changes in #1481.

• Usage and Web Search containment fixes and their populated/empty/long-content stories remain part of fix(desktop): polish list pages — Usage, Memory, and Web Search #1479.
• Memory's .settingsMemoryPreview and .settingsMemoryBackupList still overflow at the 480px floor after the shared structured-page fix exposes their true width.
• Close this issue only after Memory has no page-level horizontal overflow in the final combined state.

For that reason, #1479 should reference this issue rather than close it automatically until the remainder is complete.