feat(accounts): remove a specific account from the switcher

[shukiv]

The account switcher only offered sign out of active and sign out of all — there was no way to drop a single non-active account. That leaves you stuck if an account lands in an error state you can't switch into to sign out of.

This adds a hover × on non-active, non-default rows and a removeAccount(id) auth-store action that:

• stops the account's refresh timer and disconnects/evicts its client,
• removes it from the account registry,
• clears its per-slot session/token cookies.

Removing the active account defers to logout() (which handles switching away / redirecting). Locale keys (sidebar.remove_account, sidebar.remove_account_confirm) added to all 20 locales — English fallback for the untranslated ones.

Depends on #517 (account-switcher redesign). Until #517 merges, this PR's diff includes those commits. Rebase onto main once #517 lands.

Test plan

• Hover a non-active account → × appears; default and active rows show none.
• Click × → confirm → account leaves the switcher; active account unchanged.
• Re-add via + Add account works afterward (slot cookies were cleared).
• Removing the only other account collapses the switcher correctly.