fix: remove SDK gate from checkAvailability and add provider btn string

Remove getQueryFn() call from checkAvailability — CLI presence
and auth status are sufficient. Add custom provider button string
and spacing fix for setup screen buttons.

Author: abose

src-node/claude-code-agent.js

@@ -122,8 +122,6 @@ exports.checkAvailability = async function () {
         if (!claudePath) {
             return { available: false, claudePath: null, error: "Claude Code CLI not found" };
         }
-        // Verify the SDK can be imported
-        await getQueryFn();
         // Check if user is logged in
         let loggedIn = false;
         try {

src/nls/root/strings.js

@@ -1843,8 +1843,9 @@ define({
     "AI_CHAT_CLI_INSTALLING_MSG": "Installing Claude Code, please wait. This may take a while...",
     "AI_CHAT_CLI_RESTART_NOTE": "Restart {APP_NAME} after installation completes.",
     "AI_CHAT_CLAUDE_LOGIN_TITLE": "Setup Claude Code",
-    "AI_CHAT_CLAUDE_LOGIN_MSG": "Claude Code is installed but needs to be configured. Run the setup to sign in to your Anthropic account.",
+    "AI_CHAT_CLAUDE_LOGIN_MSG": "Claude Code is installed but needs to be configured.",
     "AI_CHAT_CLAUDE_LOGIN_BTN": "Setup Claude Code",
+    "AI_CHAT_ADD_PROVIDER_BTN": "Add Custom Provider",
     "AI_CHAT_RETRY": "Retry",
     "AI_CHAT_DESKTOP_ONLY": "AI features require the Phoenix desktop app. Download it to get started.",
     "AI_CHAT_DOWNLOAD_BTN": "Download Desktop App",

src/styles/Extn-AIChatPanel.less

@@ -1666,8 +1666,9 @@
         }
     }
 
-    .ai-install-btn {
-        margin-bottom: 8px;
+    .ai-install-btn,
+    .ai-claude-login-btn {
+        margin-bottom: 10px;
     }
 
     .ai-install-restart-note {