feat: initial x3-ssh client

- GTK3 GUI with VTE terminal emulation
- Tabbed SSH sessions
- Server management (add/edit/remove)
- SSH key management (generate/import/delete)
- Quick connect bar
- libssh for SSH connections
- autotools build system (configure && make)

.gitignore

@@ -0,0 +1,26 @@
+# Build artifacts
+*.o
+*.Po
+*.Plo
+*.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/
+
+# OS files
+.DS_Store