release: 3.0.1

Bump the workspace to 3.0.1 and bring the user guide up to date: an RDP
chapter, shell integration and inline images, SSH certificates and CAs,
known_hosts import/export, stored credentials and master password change,
profile sync (replacing the Alchementary Link migration chapter), the
Diagnostics tab and log, and refreshed screenshots throughout. The welcome
screen's protocol line now lists RDP.

docs/guide/chapters/part6-fix.tex

@@ -25,7 +25,8 @@ password, or the baud rate.
 \fix{``Host key verification failed''}{%
 The server's fingerprint changed since you last connected. That happens when a server is rebuilt, but it's also exactly
 what an attack looks like. \textbf{Check with whoever runs the server.} If it's legitimate:
-\menu{Settings\then Known Hosts}, \ui{Remove} the entry, reconnect and accept the new key.}
+choose \ui{Accept \& Update} in the warning (or \ui{Accept Once} to defer the decision). Under a Strict or Accept-new
+policy there's no prompt: \menu{Settings\then Known Hosts}, \ui{Remove} the entry and reconnect.}
 
 \fix{It just says ``Connecting…'' forever}{%
 \begin{itemize}
@@ -61,6 +62,15 @@ Check the network and the credentials, then the profile's auto-reconnect setting
   \item Connecting to a Mac? Turn on password access in macOS Screen Sharing settings (see p.\,\pageref{ch:vnc}).
 \end{itemize}}
 
+\fix{RDP won't connect}{%
+\begin{itemize}
+  \item Linux box running xrdp? Tick \ui{Allow servers without NLA}.
+  \item ``Logon failed''? Check the domain. Kerberos users: the KDC must be reachable directly, not through the proxy.
+  \item Certificate warning after a server rebuild? That's expected once; compare the fingerprint, then
+        \ui{Accept \& Update}.
+  \item Going through an RD Gateway? It needs a certificate from a public CA and Basic authentication over HTTPS.
+\end{itemize}}
+
 \section{Files}
 
 \fix{Upload is greyed out or fails}{%
@@ -86,3 +96,11 @@ normally.}
 Start Nexus Terminal with \code{--data-dir} pointing at an empty folder and try the same connection there. If it
 works, something in your profile is off; duplicate the working one and compare.
 \end{quickwin}
+
+\section{Still stuck?}
+
+\fix{Something odd that isn't on this list}{%
+Look at \code{nexus.log} in your data folder (\menu{Settings\then Diagnostics} shows where): connections, reconnects,
+host-key checks and errors, never passwords or what's on screen. Start Nexus Terminal with \code{RUST\_LOG=debug} for
+more detail. Reporting a bug? \ui{Copy Diagnostics} and paste it in.}
+