feat: server list sidebar + notifications + new icon

- Added server list sidebar (GtkPaned) showing saved servers with
  name, user@host:port detail. Double-click to connect.
- Added '+' button in sidebar to add new servers
- Added notification bar (animated GtkRevealer) for status messages:
  'Server saved', 'Server connected', 'Server disconnected',
  'Server removed', 'Key generated', 'Key imported', 'Key deleted'
  Auto-hides after 4 seconds.
- Changed icon to terminal-style PNG + SVG (scalable)
- Server list updates automatically when servers are added/removed

Layout: [Sidebar: Servers] | [Notebook: Terminal Tabs]

.gitignore

@@ -5,22 +5,15 @@
 *.lo
 x3-ssh
 
-# Autotools generated
-Makefile
-Makefile.in
-aclocal.m4
-autom4te.cache/
-build-aux/
-config.log
-config.status
-configure
-configure~
-
 # Editor files
 *~
 *.swp
 .vscode/
 .idea/
+*~
+*.swp
+.vscode/
+.idea/
 
 # OS files
 .DS_Store