feat: Integrate PR #857 dictionary intelligence and sub-activity refactor

Pull in the full feature update from PR #857 while preserving fork
advantages (HTML parsing, custom drawHints, PageForward/PageBack,
cache management, stardictCmp, /.dictionary/ paths).

- Add morphological stemming (getStemVariants), Levenshtein edit
  distance, and fuzzy matching (findSimilar) to Dictionary
- Create DictionarySuggestionsActivity for "Did you mean?" flow
- Add onDone callback to DictionaryDefinitionActivity for direct
  exit-to-reader via "Done" button
- Refactor DictionaryWordSelectActivity to ActivityWithSubactivity
  with cascading lookup (exact → stems → suggestions → not found),
  en-dash/em-dash splitting, and cross-page hyphenation
- Refactor LookedUpWordsActivity with reverse-chronological order,
  inline cascading lookup, UITheme-aware rendering, and sub-activities
- Simplify EpubReaderActivity LOOKUP/LOOKED_UP_WORDS handlers

Co-authored-by: Cursor <cursoragent@cursor.com>

src/activities/reader/DictionaryDefinitionActivity.h

@@ -14,13 +14,15 @@ class DictionaryDefinitionActivity final : public Activity {
  public:
   explicit DictionaryDefinitionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
                                         const std::string& headword, const std::string& definition, int readerFontId,
-                                        uint8_t orientation, const std::function<void()>& onBack)
+                                        uint8_t orientation, const std::function<void()>& onBack,
+                                        const std::function<void()>& onDone = nullptr)
       : Activity("DictionaryDefinition", renderer, mappedInput),
         headword(headword),
         definition(definition),
         readerFontId(readerFontId),
         orientation(orientation),
-        onBack(onBack) {}
+        onBack(onBack),
+        onDone(onDone) {}
 
   void onEnter() override;
   void onExit() override;
@@ -53,6 +55,7 @@ class DictionaryDefinitionActivity final : public Activity {
   int readerFontId;
   uint8_t orientation;
   const std::function<void()> onBack;
+  const std::function<void()> onDone;
 
   std::vector<std::vector<Segment>> wrappedLines;
   int currentPage = 0;