Add ebook reader features: view modes, dictionary, copy handler

- view-modes.ts: Paginated, scrolled, single-column, double-column modes
- dictionary-popup.ts: Dictionary lookup with popup definitions
- copy-handler.ts: Copy text with automatic citation formatting
- Add en-US.json dictionary for offline word lookups

web/static/dictionary/en-US.json

@@ -0,0 +1,8 @@
+{
+  "word": {
+    "definition": "A single distinct meaningful element of speech or writing",
+    "part_of_speech": "noun",
+    "example": "The words 'the', 'and', and 'word' are examples of words.",
+    "etymology": "Old English word, of Germanic origin; related to Dutch woord and German Wort."
+  }
+}