fix(greader): keep the trailing slash when editing an account server URL

[shajz]

What

AddGoogleReaderAccountDialog appends a trailing slash to the server URL, but the edit dialog in GoogleReaderConnection stores the value as typed. Since GoogleReaderAPI concatenates without a separator — .url("${serverUrl}accounts/ClientLogin") — editing an existing account's URL to https://example.org/api/greader.php produces a request to https://example.org/api/greader.phpaccounts/ClientLogin, and sync fails with a GoogleReaderAPIException carrying the server's raw 404 page.

The same one-liner is missing in FreshRSSConnection, whose add dialog also appends the slash.

Repro

1. Add a FreshRSS account (works — the add dialog fixes up the URL).
2. Settings → Accounts → the account → Server URL, retype it without the trailing slash.
3. Sync → 404.

This is #837, closed at the time as "seems fixed" but still reproducible on main.

Fix

Normalize on save in both connection screens, the way the add dialogs already do — same shape as #357, which fixed the equivalent Fever bug in both the add and the edit path.