v1.8.3: session pool + sidebar indicators

- SessionPool: LRU cache for SSH/SFTP sessions across server switches
- Sidebar: green dot indicators for servers with active sessions
- Sidebar: active sessions count label
- Terminal: buffer preservation on server switch via get_current_buffer()
- FilesTab/TerminalTab: pool integration for session reuse

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/widgets/terminal_widget.py

@@ -361,6 +361,23 @@ class TerminalWidget(tk.Frame):
     def get_size(self) -> tuple[int, int]:
         return self._cols, self._rows
 
+    def get_current_buffer(self) -> bytes:
+        """Export current pyte screen content as ANSI bytes for session pool preservation."""
+        screen = self._screen
+        lines = []
+        for row in range(screen.lines):
+            line = screen.buffer[row]
+            chars = []
+            for col in range(screen.columns):
+                chars.append(line[col].data)
+            # Strip trailing spaces
+            text = "".join(chars).rstrip()
+            lines.append(text)
+        # Remove trailing empty lines
+        while lines and not lines[-1]:
+            lines.pop()
+        return "\n".join(lines).encode("utf-8")
+
     # ── Rendering ──────────────────────────────────────────────────────────
 
     def _render(self):