Release v3.8: New profile (blank template renamed), password-mismatch warning stays up, IP-pinning docs

New profile: a File-menu item + Ctrl+N that loads a fresh blank template as a
new unsaved session via a LoadBlankTemplateNext handoff to Program.cs's relaunch
loop — reachable even when "start with a specific profile" boots past the picker
(issue #6). Offers to save the current profile first if dirty; deliberately
silent (no profile-switch cue).

Renamed the user-facing "blank template" to "New profile": the picker's synthetic
entry (now a distinct marker TYPE, collision-safe against a real profile named
"New profile"), the window title ("RemSound — New profile"), and the manual.

Fixed the password-mismatch warning flashing away: it's raised from the 1 Hz
statusTimer, which kept firing into the modal loop and rebuilt the peer lists
(SyncAllPeerLists) under the dialog, knocking it out of the foreground. Now the
tick is frozen while it's up, it's routed through ForegroundDialog, and a
re-entry guard ensures one warning that stays put. Audited: it was the only
popup raised from a recurring timer.

Docs: manual section "Connecting to one specific IP address (and only that one)"
explaining by-name vs by-fixed-IP and that a profile saves the exact address
(issue #7 — functionality already existed); About box + RELEASE_NOTES for v3.8;
MANUAL.md regenerated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/AboutDialog.cs

@@ -20,6 +20,23 @@ internal sealed class AboutDialog : Form
     /// updates" path.</summary>
     private const string ReleaseNotes =
         """
+        RemSound v3.8
+
+        You can now start a brand-new profile at any time. A
+        new "New profile" item at the top of the File menu (or
+        Ctrl+N) opens a fresh, unsaved profile, so you can set up
+        a profile for a different connection from scratch — even
+        when RemSound is set to start straight into a specific
+        profile and you'd otherwise never see the picker. If your
+        current profile has unsaved changes, it offers to save
+        them first. The startup picker and the window title now
+        say "New profile" too, where they used to say "blank
+        template".
+
+        And the "you and the other person have different
+        passwords" warning now stays on screen until you press
+        OK, instead of flashing away before you could reach it.
+
         RemSound v3.7
 
         Changing audio devices mid-session is smoother. A quick