feat: add account search to account list

[Jeakcey]

What changed

• add a compact account search field when 8 or more accounts are saved
• filter both the active account and other account cards by custom name or email, case-insensitively
• preserve the existing account sort order and actions while showing matching counts and a no-results state

Why

This addresses the real-world multi-account workflow described in #101 without adding UI clutter for the common 2–3 account case.

Impact

• the search runs entirely in the shared React frontend, including the Windows app
• saved account data, backend commands, switching behavior, and sorting are unchanged
• clearing the query immediately restores the full account list

Checks

• pnpm build (tsc && vite build)
• full Windows Tauri release build with Rust/MSVC: generated the app executable plus MSI and NSIS bundles
• updater-artifact signing was disabled only for the local build because the maintainer signing private key is intentionally unavailable
• Windows release-app smoke test with 28 real accounts:
  • custom-name search returned the expected single account
  • uppercase email fragment with leading/trailing spaces matched case-insensitively
  • clearing restored 1 active + 27 other accounts
  • a non-matching query displayed the no-results state
  • changing sort order, filtering, and restoring the original sort all behaved correctly

No screenshots are attached because the real account list contains private email addresses.

[emreertunc]

Thanks for the implementation. I found one edge case that needs to be fixed before approval.

When a search query is active and the account count drops from 8 to 7, the search input is hidden because the threshold is no longer met, but the query remains active and continues filtering the account list.

For example, with exactly 8 accounts, search for an account that is the only match and then delete it. The UI displays “No matching accounts,” while the search field and its clear button are no longer available.

Please clear the query or disable filtering whenever the account count falls below the search threshold.

[Jeakcey]

Addressed the requested 8 -> 7 account edge case in commit 25a32b0.

• Filtering is disabled immediately whenever the total account count falls below the 8-account search threshold.
• The stale search query is also cleared when search becomes unavailable, so it cannot reactivate unexpectedly later.
• Reproduced the pre-fix failure with an isolated mocked 8-account UI: search for the only matching account, delete it, and the page became stuck on No matching accounts with no search control.
• Re-ran the identical flow after the fix: the search control is hidden, the query is cleared, and all 7 remaining accounts are shown.
• Validation passed: pnpm build and a full Windows Tauri release build (EXE, MSI, and NSIS; updater artifact signing disabled only in the local build config because the maintainer signing key is not available).

The PR head is now 25a32b0 and is ready for re-review.

[emreertunc]

Thanks for the contribution!