feat: multi-type server support — SQL, Redis, Grafana, Prometheus, Telnet, WinRM, RDP/VNC

Full implementation of multi-type server management across GUI and CLI:

New clients: SQLClient (MariaDB/MSSQL/PostgreSQL), RedisClient, GrafanaClient,
PrometheusClient, TelnetSession, WinRMClient, RemoteDesktopLauncher.

New GUI tabs: QueryTab (SQL editor + Treeview), RedisTab (console + history),
GrafanaTab (dashboards + alerts), PrometheusTab (PromQL + targets),
PowershellTab (PS/CMD), LaunchTab (RDP/VNC external client).

Infrastructure: TAB_REGISTRY for conditional tabs per server type,
adaptive server_dialog fields, colored type badges in sidebar,
status checker for all types (SSH/TCP/SQL/Redis/HTTP), 100+ i18n keys.

CLI: ssh.py extended with --sql, --redis, --grafana-*, --prom-*, --ps, --cmd.

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

gui/tabs/terminal_tab.py

@@ -1,5 +1,5 @@
 """
-Terminal tab — persistent interactive SSH shell via ShellSession + TerminalWidget.
+Terminal tab — persistent interactive SSH/Telnet shell via ShellSession/TelnetSession + TerminalWidget.
 """
 
 import queue
@@ -8,6 +8,7 @@ import threading
 import time
 import customtkinter as ctk
 from core.ssh_client import ShellSession
+from core.telnet_client import TelnetSession
 from core.i18n import t
 
 # Regex to strip ANSI escape sequences
@@ -20,7 +21,7 @@ class TerminalTab(ctk.CTkFrame):
         self.store = store
         self.session_pool = session_pool
         self._current_alias: str | None = None
-        self._session: ShellSession | None = None
+        self._session: ShellSession | TelnetSession | None = None
         self._reconnect_count = 0
         self._max_reconnect = 5
         self._intentional_disconnect = False
@@ -76,16 +77,25 @@ class TerminalTab(ctk.CTkFrame):
             return
 
         alias = self._current_alias
+        server_type = server.get("type", "ssh")
         self._terminal.set_status(t("term_connecting").format(alias=alias), "#ccaa00")
         self._intentional_disconnect = False
 
         def _do_connect():
             try:
                 key_path = self.store.get_ssh_key_path()
+                cols, rows = self._terminal.get_size()
 
-                # Use session pool if available
-                if self.session_pool:
-                    cols, rows = self._terminal.get_size()
+                if server_type == "telnet":
+                    # Telnet — direct session, no pool (pool is SSH-specific)
+                    self.after(0, self._terminal.reset)
+                    session = TelnetSession(server, cols=cols, rows=rows)
+                    session.on_data = self._on_data_received
+                    session.on_disconnect = self._on_disconnected
+                    session.connect()
+                    self._session = session
+                elif self.session_pool:
+                    # SSH with session pool
                     session, is_new = self.session_pool.get_or_create_shell_session(alias, server, key_path)
                     if is_new:
                         # New session — reset terminal for clean start
@@ -108,9 +118,8 @@ class TerminalTab(ctk.CTkFrame):
                     session.on_disconnect = self._on_disconnected
                     self._session = session
                 else:
-                    # Legacy behavior without session pool
+                    # SSH without pool (legacy)
                     self.after(0, self._terminal.reset)
-                    cols, rows = self._terminal.get_size()
                     session = ShellSession(server, key_path, cols=cols, rows=rows)
                     session.on_data = self._on_data_received
                     session.on_disconnect = self._on_disconnected
@@ -136,12 +145,18 @@ class TerminalTab(ctk.CTkFrame):
 
     def _disconnect(self):
         self._intentional_disconnect = True
-        # Only disconnect if we don't have a session pool (otherwise session stays alive)
-        if not self.session_pool and self._session:
+        if not self._session:
+            return
+        # Telnet sessions are never pooled — always disconnect directly
+        if isinstance(self._session, TelnetSession):
             self._session.disconnect()
             self._session = None
-        # If using session pool, session remains active in the pool
-        elif self.session_pool and self._session:
+        # SSH without session pool — disconnect directly
+        elif not self.session_pool:
+            self._session.disconnect()
+            self._session = None
+        # SSH with session pool — session remains active in the pool
+        else:
             # Remove callbacks to prevent processing data after switch
             self._session.on_data = None
             self._session.on_disconnect = None