feat(web-ui): add bandwidth unit toggle (Mbps / MB/s) on status page

[stackia]

Summary

• Adds a Mbps / MB/s unit selector to the status header. Default Mbps; choice persists in localStorage and is applied to every bandwidth readout (header total, per-client table, per-worker stats).
• Factors the shared "persisted enum" pattern out of useTheme, useLocale, and the new useBandwidthUnit into a single usePersistedEnum hook. Also fixes an inherited no-op localStorage write on mount.
• Extracts a HeaderSelect helper inside StatusHeader to dedupe the three icon + label + SelectBox blocks (Language / Appearance / Bandwidth Unit).

Screenshots

The bandwidth unit dropdown sits to the right of Appearance and follows the same icon + label + dropdown pattern. On narrow screens it wraps to a second row, right-aligned to line up under Appearance.

Test plan

• Open the status page — verify the new "带宽单位 / Bandwidth Unit / 頻寬單位" dropdown appears next to Appearance.
• Switch the unit; the header total, every connection row, and every worker card should update from Mbps to MB/s (and back).
• Reload the page — selection persists.
• Switch back to default (Mbps) and reload — verify the status-bandwidth-unit localStorage key is removed (not stored as default).
• Resize the window from wide to narrow — the wrapped row should stay right-aligned.
• Switch language / theme — they still persist correctly (regression check on the refactored hooks).

🤖 Generated with Claude Code

[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://thankful-water-0a297bf00-467.eastasia.1.azurestaticapps.net

[Copilot]

Pull request overview

Adds a user-selectable bandwidth display unit (Mbps vs MB/s) to the Web UI status page and refactors “persisted enum” localStorage logic into a shared hook so theme/locale/unit preferences persist consistently.

Changes:

• Add a Bandwidth Unit selector in the status header and propagate the selection to all bandwidth readouts (total, per-client, per-worker).
• Introduce usePersistedEnum and refactor useTheme / useLocale (and new useBandwidthUnit) to use it, avoiding redundant localStorage writes.
• Update shared typing/i18n to support the new selector and stronger enum-style type definitions.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
web-ui/src/types/ui.ts	Introduces THEME_MODES and adds BANDWIDTH_UNITS + BandwidthUnit type for shared UI enums.
web-ui/src/pages/status.tsx	Wires useBandwidthUnit into the status page and passes the selected unit through to header/sections; updates total bandwidth formatting.
web-ui/src/lib/locale.ts	Converts supported locales to a as const tuple and removes now-obsolete locale init helpers (replaced by persisted-enum hook usage).
web-ui/src/lib/format.ts	Updates formatBandwidth to accept a BandwidthUnit and format as Mbps (bits) or MB/s (bytes).
web-ui/src/i18n/status.ts	Adds translated label key for the new “Bandwidth Unit” selector.
web-ui/src/hooks/use-theme.ts	Refactors theme persistence to usePersistedEnum and removes redundant localStorage writes.
web-ui/src/hooks/use-persisted-enum.ts	Adds shared hook to persist validated string-enum selections with “don’t store default” behavior.
web-ui/src/hooks/use-locale.ts	Refactors locale persistence to usePersistedEnum, using browser-detected locale as the default baseline.
web-ui/src/hooks/use-bandwidth-unit.ts	Adds new persisted bandwidth-unit hook built on usePersistedEnum.
web-ui/src/components/status/workers-section.tsx	Threads bandwidth unit into worker stats formatting.
web-ui/src/components/status/status-header.tsx	Adds the bandwidth unit dropdown and deduplicates header select rendering via HeaderSelect.
web-ui/src/components/status/connections-section.tsx	Threads bandwidth unit into per-client bandwidth formatting (table + mobile cards).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.