feat: add request history

[slverma]

Description:

Summary

• Adds request history: every send (success or network failure) is recorded, viewable per-request in a new History tab on the request editor, and across the whole workspace in a new full-width History panel (opened from a button in the sidebar).
• History entries can be expanded to inspect the full request/response, restored back into the live request (writes the raw, pre-interpolation config so {{variables}} and folder baseUrl aren't frozen in), or deleted individually / cleared in bulk.
• Storage is capped (20 entries per request, 200 globally, 200KB per body) and pruned automatically via a new HistoryManager.
• A "Enable History" toggle in the History panel lets users pause recording without losing anything already saved.

Notable design decisions

• The global History view was originally an in-sidebar section but was relocated to its own singleton editor-panel tab (matching how request/folder editors already open) after the sidebar proved too narrow for a good reading experience — this required a new 4th Vite-built webview bundle (src/webview/history/).
• Restore intentionally writes the raw (pre-interpolation, pre-baseUrl) request snapshot, not the fully-resolved URL that was actually sent — restoring resolved values would double-prepend the folder's base URL and bake {{variables}} into literal strings.
• The enable/disable flag lives entirely inside HistoryManager, so no caller needs to know it exists — addEntry just silently no-ops while paused; delete/clear remain fully functional regardless of the flag.

Test plan

• npx tsc --noEmit passes (verified throughout; no test suite exists in this repo)
• Send a few requests (mix successes and at least one network failure) and confirm entries appear in both the per-request History tab and the global History panel
• Expand an entry, confirm request/response detail renders correctly
• Restore an older entry and confirm the form updates and shows unsaved (per-request tab) or persists immediately (global panel)
• Delete an entry and Clear All from both surfaces; confirm the other surface stays in sync
• Delete the underlying request, then confirm restoring its orphaned global-history entry shows a warning instead of restoring
• Toggle "Enable History" off, send a request, confirm nothing new is recorded; toggle back on and confirm recording resumes
• Confirm the toggle's state persists across reopening the History panel