Button to save device to user settings

Add UI and functionality to the Devices panel to support adding a new device to the list. Users should be able to click an "Add" button in the Devices panel, which will:

1. Prompt where to save the device config

   • Options: user, folder, or workspace scope. something like this:
   

2. Collect device information

   • Fields: ip address (host), password (optional), nickname (optional), and any other relevant device fields.

3. Write device structure

   • Compose device config and save it under the selected config scope (brightscript.devices setting).

Example configuration:

{
  "host": "192.168.1.100",
  "name": "Bedroom Roku",
  "password": "myroku123"
}

Structure and Requirements

• Follow the merging and hierarchy logic described in Issue #690:
  • Support all VSCode configuration scopes (user, workspace, folder, etc), using "last one in wins" priority.
  • If duplicate device IDs exist, properties should be merged, following the config priority order.
  • Configuration UI should clarify where the device is being saved and potential overrides.
• The "Add Device" UI/flow must:
  • Save the device such that it appears in the device list.
  • Respect config merging and deduplication rules per #690.
  • Validate and prompt for all required fields (at minimum: IP address/host).

Acceptance Criteria:

• An "Add Device" button appears in the Devices panel.
• Users are prompted for save location (scope) and device details.
• Device configuration is correctly written and merged across all config scopes.
• Device appears in the list immediately after addition.
• No duplicates; merging follows the hierarchy outlined in #690.

See reference: #690 for merging rules and structure.