feat(server): add configurable SSH connection timeout per server

Add `connection_timeout` field to server settings, allowing per-server
override of the global SSH connection timeout constant.

- Migration adds `connection_timeout` integer column (default 10s)
- `ServerSetting` model exposes and casts the new field
- `SshMultiplexingHelper::getConnectionTimeout()` resolves per-server
  value with fallback to `constants.ssh.connection_timeout`
- All SSH/SCP command builders use the new resolver instead of the
  global config directly
- Livewire `Show` component binds `connectionTimeout` with validation
  (1–300 seconds) and syncs to/from the model
- UI input added to server settings form with helper text
- Feature tests cover default, persistence, resolver, and fallback

resources/views/livewire/server/show.blade.php

@@ -191,6 +191,12 @@
                                 label="Port" required :disabled="$isValidating" />
                         </div>
                     </div>
+                    <div class="w-full lg:w-64">
+                        <x-forms.input canGate="update" :canResource="$server" type="number"
+                            id="connectionTimeout" label="SSH Connection Timeout (s)"
+                            helper="Seconds to wait for SSH connection before failing. Default: 10."
+                            min="1" max="300" required :disabled="$isValidating" />
+                    </div>
                     <div class="w-full">
                         <div class="flex items-center mb-1">
                             <label for="serverTimezone">Server Timezone</label>