fix: Header display, mode toggle, and help screen improvements

- Fix toggle_mode to pass envelope context when reloading (preserves compression)
- Add CSS for header labels: single-line with text-overflow ellipsis
- Add 'full-headers' CSS class for toggling between compressed/full view
- Store full subject in header for proper refresh on toggle
- Update HelpScreen with missing shortcuts (o, b) and better descriptions
- Fix duplicate line in _refresh_display

src/mail/email_viewer.tcss

@@ -73,10 +73,25 @@ StatusTitle {
 EnvelopeHeader {
   dock: top;
   width: 100%;
-  max-height: 2;
+  height: auto;
+  max-height: 10;
+  padding: 0 1;
   tint: $primary 10%;
 }
 
+/* Header labels should be single line with truncation */
+EnvelopeHeader Label {
+  width: 100%;
+  height: 1;
+  text-overflow: ellipsis;
+}
+
+/* Full headers mode - allow wrapping */
+EnvelopeHeader.full-headers Label {
+  height: auto;
+  text-overflow: clip;
+}
+
 Markdown {
   padding: 1 2;
 }

src/mail/screens/HelpScreen.py

@@ -66,10 +66,12 @@ class HelpScreen(Screen):
             yield Static("  j/k    - Next/Previous message")
             yield Static("  g      - Go to oldest message")
             yield Static("  G      - Go to newest message")
+            yield Static("  b      - Scroll page up")
             yield Static("  PageDown/PageUp - Scroll page down/up")
             yield Static("")
 
             yield Static("[b green]Message Actions[/b green]")
+            yield Static("  o      - Open message externally")
             yield Static("  #      - Delete message(s)")
             yield Static("  e      - Archive message(s)")
             yield Static("  u      - Toggle read/unread")
@@ -79,8 +81,10 @@ class HelpScreen(Screen):
 
             yield Static("[b green]View Options[/b green]")
             yield Static("  w      - Toggle message view window")
-            yield Static("  m      - Toggle markdown/html view mode")
-            yield Static("  h      - Toggle envelope header")
+            yield Static(
+                "  m      - Toggle markdown/html view (or compressed/html for notifications)"
+            )
+            yield Static("  h      - Toggle full/compressed envelope headers")
             yield Static("")
 
             yield Static("[b green]Search & Filter[/b green]")

src/mail/widgets/ContentContainer.py

@@ -122,12 +122,13 @@ class EnvelopeHeader(Vertical):
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
-        self.subject_label = Label("")
-        self.from_label = Label("")
-        self.to_label = Label("")
-        self.date_label = Label("")
-        self.cc_label = Label("")
+        self.subject_label = Label("", id="header_subject")
+        self.from_label = Label("", id="header_from")
+        self.to_label = Label("", id="header_to")
+        self.date_label = Label("", id="header_date")
+        self.cc_label = Label("", id="header_cc")
         # Store full values for toggle
+        self._full_subject = ""
         self._full_to = ""
         self._full_cc = ""
         self._full_from = ""
@@ -212,18 +213,30 @@ class EnvelopeHeader(Vertical):
     def toggle_full_headers(self) -> None:
         """Toggle between compressed and full header view."""
         self.show_full_headers = not self.show_full_headers
+        # Update CSS class for styling
+        if self.show_full_headers:
+            self.add_class("full-headers")
+        else:
+            self.remove_class("full-headers")
         self._refresh_display()
 
     def _refresh_display(self) -> None:
         """Refresh the display based on current mode."""
         if self.show_full_headers:
+            # Full view - show complete text
+            self.subject_label.update(
+                f"[b bright_white]{self._full_subject}[/b bright_white]"
+            )
             self.from_label.update(f"[b]From:[/b] {self._full_from}")
             self.to_label.update(f"[b]To:[/b] {self._full_to}")
             if self._full_cc:
                 self.cc_label.update(f"[b]CC:[/b] {self._full_cc}")
                 self.cc_label.styles.display = "block"
         else:
-            # Compressed view
+            # Compressed view - truncate for single line display
+            self.subject_label.update(
+                f"[b bright_white]{self._full_subject}[/b bright_white]"
+            )
             self.from_label.update(
                 f"[b]From:[/b] {self._compress_recipients(self._full_from, max_shown=1)}"
             )
@@ -238,13 +251,11 @@ class EnvelopeHeader(Vertical):
 
     def update(self, subject, from_, to, date, cc=None):
         # Store full values
+        self._full_subject = subject or ""
         self._full_from = from_ or ""
         self._full_to = to or ""
         self._full_cc = cc or ""
 
-        # Subject is prominent - bold, bright white, no label needed
-        self.subject_label.update(f"[b bright_white]{subject}[/b bright_white]")
-
         # Format the date for better readability
         if date:
             try:
@@ -334,15 +345,25 @@ class ContentContainer(ScrollableContainer):
         self.border_subtitle = f"{mode_icon} {mode_label}"
 
     async def action_toggle_mode(self):
-        """Toggle between markdown and HTML viewing modes."""
+        """Toggle between markdown/compressed and HTML viewing modes.
+
+        For notification emails: cycles between compressed view and HTML.
+        For regular emails: cycles between markdown and HTML.
+        """
         if self.current_mode == "html":
             self.current_mode = "markdown"
         else:
             self.current_mode = "html"
 
         # Reload the content if we have a message ID
+        # This will re-apply compression if applicable for markdown mode
         if self.current_message_id:
-            self.display_content(self.current_message_id)
+            self.display_content(
+                self.current_message_id,
+                folder=self.current_folder,
+                account=self.current_account,
+                envelope=self.current_envelope,
+            )
 
     def update_header(self, subject, from_, to, date, cc=None):
         self.header.update(subject, from_, to, date, cc)