Add popup notifications, log view (F5) and context-sensitive key hints (M9)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/ui/help.go

@@ -6,7 +6,7 @@ import (
 )
 
 const helpText = `[yellow]Global[-]
-  F1-F4                  switch view
+  F1-F5                  switch view
   Tab, Shift+Tab         switch panel within a view
   ?, F9                  this help (F9 works while typing)
   q, Ctrl+C              quit
@@ -43,6 +43,10 @@ const helpText = `[yellow]Global[-]
   t                      retry a failed download (history)
   r                      refresh now
 
+[yellow]Log (F5)[-]
+  Popups fade away by themselves; everything they said is kept here.
+  ↑↓, PgUp/PgDn          scroll        G  follow new entries        c  clear
+
 [yellow]Connections[-]
 `