Actually fix oversized PDF text — root cause was the previous fix

Empirically reproduced this outside the app (standalone WKWebView +
createPDF script, inspecting real PDF page bounds via PDFKit) instead
of guessing again. Findings:

- WKPDFConfiguration.rect left at default captures the webview's
  frame size verbatim when content fits within it, and auto-grows to
  a single tall page matching full scrollable content when it
  overflows. It does not paginate, and setting rect explicitly just
  clips to that one rect instead.
- The scrollHeight-based frame resize added last round (to "fix" this
  same bug) was itself the problem: resizing the frame before calling
  createPDF produced a page that didn't match the resized frame at
  all (e.g. resized to 816x295, captured page came out 799x375) — a
  small, badly-proportioned page that made ordinarily-sized text look
  enormous relative to it. Removed entirely.
- A visible scrollbar during capture shaves ~17pt off the captured
  page width. Added ::-webkit-scrollbar { display: none } to prevent
  that.

Verified against a 12-message realistic conversation: clean single
page, correct proportions, readable text, matches the intended CSS
layout. The text-size-adjust/viewport-meta fix from last round turned
out to be unnecessary (computed font-size was correct all along) but
is harmless, so left in place.

oAI/Services/ConversationExportService.swift

@@ -71,6 +71,7 @@ enum ConversationExportService {
     nonisolated private static let css = """
     :root { color-scheme: light dark; }
     html { -webkit-text-size-adjust: 100%; text-size-adjust: 100%; }
+    ::-webkit-scrollbar { display: none; }
     body { font-family: -apple-system, BlinkMacSystemFont, "Helvetica Neue", sans-serif; \
     font-size: 15px; color: #1a1a1a; background: #ffffff; max-width: 820px; margin: 40px auto; \
     padding: 0 24px; line-height: 1.5; }
@@ -113,7 +114,15 @@ enum ConversationExportService {
 
     static func pdfData(name: String, messages: [Message]) async throws -> Data {
         let htmlString = html(name: name, messages: messages)
-        let webView = WKWebView(frame: NSRect(x: 0, y: 0, width: 816, height: 1056))
+        // Confirmed empirically (not guessed): with WKPDFConfiguration.rect left at its
+        // default, createPDF captures exactly the webview's frame size verbatim for content
+        // that fits within it, and auto-grows to a single tall page matching the full
+        // scrollable content when it overflows — it does not paginate. Manually resizing the
+        // frame to match content height beforehand (a previous attempt at this) actively
+        // breaks that: the captured page ends up NOT matching the resized frame at all,
+        // producing a small, oddly-proportioned page that made ordinary-sized text look
+        // enormous relative to it. So: set a sane starting frame and leave it alone.
+        let webView = WKWebView(frame: NSRect(x: 0, y: 0, width: 850, height: 1100))
         webView.pageZoom = 1.0
         // PDF content is baked at export time, so it can't respond to prefers-color-scheme
         // live like the HTML export does — match whatever appearance the app is in right now.
@@ -122,14 +131,6 @@ enum ConversationExportService {
         webView.navigationDelegate = delegate
         try await delegate.load(htmlString, in: webView)
 
-        // Resize to the actual rendered content height so createPDF's capture bounds match
-        // reality, rather than relying on its undocumented auto-sizing against the arbitrary
-        // initial frame — a mismatch here is a common cause of blown-up/rescaled PDF output.
-        if let heightValue = try? await webView.evaluateJavaScript("document.body.scrollHeight"),
-           let height = (heightValue as? NSNumber)?.doubleValue, height > 0 {
-            webView.frame = NSRect(x: 0, y: 0, width: webView.frame.width, height: height)
-        }
-
         return try await withCheckedThrowingContinuation { continuation in
             webView.createPDF(configuration: WKPDFConfiguration()) { result in
                 continuation.resume(with: result)