feat: rewrite terminal to use vte_terminal_spawn_sync

Replaced the SSH library + IO thread + intermediate PTY bridge with
vte_terminal_spawn_sync(). This eliminates the broken terminal behavior
(backspace, Ctrl+C, copy/paste, bash completion) caused by the
intermediate PTY with no process on the slave side.

- SshTerminal now spawns 'ssh' as a VTE subprocess
- Removed libssh dependency from terminal (still used for key validation)
- Removed IO thread, manual PTY creation, and thread synchronization
- VTE now handles all terminal I/O, line discipline, resize, etc.
- Password saved: uses sshpass -e with SSHPASS env var if available
- Password not saved: ssh prompts interactively in the terminal
- Removed show_password_dialog (no longer needed)
- Simplified connect flow in ssh_client.cpp

configure

@@ -613,8 +613,6 @@ ac_subst_vars='am__EXEEXT_FALSE
 am__EXEEXT_TRUE
 LTLIBOBJS
 LIBOBJS
-LIBSSH_LIBS
-LIBSSH_CFLAGS
 VTE_LIBS
 VTE_CFLAGS
 GTK_LIBS
@@ -732,9 +730,7 @@ PKG_CONFIG_LIBDIR
 GTK_CFLAGS
 GTK_LIBS
 VTE_CFLAGS
-VTE_LIBS
-LIBSSH_CFLAGS
-LIBSSH_LIBS'
+VTE_LIBS'
 
 
 # Initialize some variables set by options.
@@ -1382,9 +1378,6 @@ Some influential environment variables:
   GTK_LIBS    linker flags for GTK, overriding pkg-config
   VTE_CFLAGS  C compiler flags for VTE, overriding pkg-config
   VTE_LIBS    linker flags for VTE, overriding pkg-config
-  LIBSSH_CFLAGS
-              C compiler flags for LIBSSH, overriding pkg-config
-  LIBSSH_LIBS linker flags for LIBSSH, overriding pkg-config
 
 Use these variables to override the choices made by 'configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -5120,97 +5113,6 @@ printf "%s\n" "yes" >&6; }
 
 fi
 
-pkg_failed=no
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for libssh >= 0.9" >&5
-printf %s "checking for libssh >= 0.9... " >&6; }
-
-if test -n "$LIBSSH_CFLAGS"; then
-    pkg_cv_LIBSSH_CFLAGS="$LIBSSH_CFLAGS"
- elif test -n "$PKG_CONFIG"; then
-    if test -n "$PKG_CONFIG" && \
-    { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libssh >= 0.9\""; } >&5
-  ($PKG_CONFIG --exists --print-errors "libssh >= 0.9") 2>&5
-  ac_status=$?
-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
-  test $ac_status = 0; }; then
-  pkg_cv_LIBSSH_CFLAGS=`$PKG_CONFIG --cflags "libssh >= 0.9" 2>/dev/null`
-		      test "x$?" != "x0" && pkg_failed=yes
-else
-  pkg_failed=yes
-fi
- else
-    pkg_failed=untried
-fi
-if test -n "$LIBSSH_LIBS"; then
-    pkg_cv_LIBSSH_LIBS="$LIBSSH_LIBS"
- elif test -n "$PKG_CONFIG"; then
-    if test -n "$PKG_CONFIG" && \
-    { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"libssh >= 0.9\""; } >&5
-  ($PKG_CONFIG --exists --print-errors "libssh >= 0.9") 2>&5
-  ac_status=$?
-  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
-  test $ac_status = 0; }; then
-  pkg_cv_LIBSSH_LIBS=`$PKG_CONFIG --libs "libssh >= 0.9" 2>/dev/null`
-		      test "x$?" != "x0" && pkg_failed=yes
-else
-  pkg_failed=yes
-fi
- else
-    pkg_failed=untried
-fi
-
-
-
-if test $pkg_failed = yes; then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-
-if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
-        _pkg_short_errors_supported=yes
-else
-        _pkg_short_errors_supported=no
-fi
-        if test $_pkg_short_errors_supported = yes; then
-                LIBSSH_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "libssh >= 0.9" 2>&1`
-        else
-                LIBSSH_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "libssh >= 0.9" 2>&1`
-        fi
-        # Put the nasty error message in config.log where it belongs
-        echo "$LIBSSH_PKG_ERRORS" >&5
-
-        as_fn_error $? "Package requirements (libssh >= 0.9) were not met:
-
-$LIBSSH_PKG_ERRORS
-
-Consider adjusting the PKG_CONFIG_PATH environment variable if you
-installed software in a non-standard prefix.
-
-Alternatively, you may set the environment variables LIBSSH_CFLAGS
-and LIBSSH_LIBS to avoid the need to call pkg-config.
-See the pkg-config man page for more details." "$LINENO" 5
-elif test $pkg_failed = untried; then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-        { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: error: in '$ac_pwd':" >&5
-printf "%s\n" "$as_me: error: in '$ac_pwd':" >&2;}
-as_fn_error $? "The pkg-config script could not be found or is too old.  Make sure it
-is in your PATH or set the PKG_CONFIG environment variable to the full
-path to pkg-config.
-
-Alternatively, you may set the environment variables LIBSSH_CFLAGS
-and LIBSSH_LIBS to avoid the need to call pkg-config.
-See the pkg-config man page for more details.
-
-To get pkg-config, see <http://pkg-config.freedesktop.org/>.
-See 'config.log' for more details" "$LINENO" 5; }
-else
-        LIBSSH_CFLAGS=$pkg_cv_LIBSSH_CFLAGS
-        LIBSSH_LIBS=$pkg_cv_LIBSSH_LIBS
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-
-fi
-
 ac_config_files="$ac_config_files Makefile src/Makefile"
 
 cat >confcache <<\_ACEOF