smart context v3 (#1022)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Adds Smart Context v3 with selectable modes (Off, Conservative,
Balanced) and surfaces token savings in chat. Also improves token
estimation by counting per-file tokens when Smart Context is enabled.

- **New Features**
- Smart Context selector in Pro settings with three options.
Conservative is the default when enabled without an explicit choice.
- New setting: proSmartContextOption ("balanced"); undefined implies
Conservative.
- Engine now receives enable_smart_files_context and smart_context_mode.
- Chat shows a DyadTokenSavings card when the message contains
token-savings?original-tokens=...&smart-context-tokens=..., with percent
saved and a tooltip for exact tokens.
- Token estimation uses extracted file contents for accuracy when Pro +
Smart Context is on; otherwise falls back to formatted codebase output.

<!-- End of auto-generated description by cubic. -->

src/ipc/handlers/token_count_handlers.ts

@@ -86,13 +86,23 @@ export function registerTokenCountHandlers() {
 
       if (chat.app) {
         const appPath = getDyadAppPath(chat.app.path);
-        codebaseInfo = (
-          await extractCodebase({
-            appPath,
-            chatContext: validateChatContext(chat.app.chatContext),
-          })
-        ).formattedOutput;
-        codebaseTokens = estimateTokens(codebaseInfo);
+        const { formattedOutput, files } = await extractCodebase({
+          appPath,
+          chatContext: validateChatContext(chat.app.chatContext),
+        });
+        codebaseInfo = formattedOutput;
+        if (settings.enableDyadPro && settings.enableProSmartFilesContextMode) {
+          codebaseTokens = estimateTokens(
+            files
+              // It doesn't need to be the exact format but it's just to get a token estimate
+              .map(
+                (file) => `<dyad-file=${file.path}>${file.content}</dyad-file>`,
+              )
+              .join("\n\n"),
+          );
+        } else {
+          codebaseTokens = estimateTokens(codebaseInfo);
+        }
         logger.log(
           `Extracted codebase information from ${appPath}, tokens: ${codebaseTokens}`,
         );