refactor(domain): add prepare_text_for_tts — unified normalization pipeline

New function chains all three normalization stages:
  1. Heteronym sentence rules (context-dependent pronunciation)
  2. Pronunciation rules (token-level replacements)
  3. Pipeline normalization (apostrophe, LLM)

This is the single entry point that both Web UI and PyQt should call
before TTS synthesis. Currently only Web UI uses it; PyQt has NO
normalization — this unlocks that capability.

Updated conversion_runner.emit_text to use the new function.
1038 tests pass.

tests/test_domain_normalization_pipeline.py

@@ -0,0 +1,147 @@
+"""Tests for domain/normalization.py — prepare_text_for_tts."""
+
+import pytest
+from unittest.mock import patch, MagicMock
+from abogen.domain.normalization import prepare_text_for_tts, normalize_text_for_pipeline
+
+
+class TestPrepareTextForTts:
+    """Tests for the comprehensive TTS text preparation pipeline."""
+
+    def test_empty_text(self):
+        result = prepare_text_for_tts("")
+        assert result == ""
+
+    def test_none_text(self):
+        result = prepare_text_for_tts(None)
+        assert result == ""
+
+    def test_passthrough_no_rules(self):
+        result = prepare_text_for_tts("Hello world")
+        assert isinstance(result, str)
+        assert len(result) > 0
+
+    def test_heteronym_rules_applied(self):
+        from abogen.domain.pronunciation import compile_heteronym_sentence_rules
+
+        overrides = [
+            {
+                "token": "read",
+                "pronunciation": "red",
+                "context": "past tense",
+            }
+        ]
+        rules = compile_heteronym_sentence_rules(overrides)
+        if rules:
+            result = prepare_text_for_tts("I will read the book", heteronym_rules=rules)
+            assert isinstance(result, str)
+
+    def test_pronunciation_rules_applied(self):
+        from abogen.domain.pronunciation import compile_pronunciation_rules
+
+        overrides = [
+            {
+                "token": "epub",
+                "pronunciation": "ee-pub",
+                "normalized": "epub",
+            }
+        ]
+        rules = compile_pronunciation_rules(overrides)
+        result = prepare_text_for_tts(
+            "This is an epub file",
+            pronunciation_rules=rules,
+        )
+        assert "ee-pub" in result
+
+    def test_usage_counter_tracks_pronunciation(self):
+        from abogen.domain.pronunciation import compile_pronunciation_rules
+
+        overrides = [
+            {
+                "token": "data",
+                "pronunciation": "day-ta",
+                "normalized": "data",
+            }
+        ]
+        rules = compile_pronunciation_rules(overrides)
+        counter = {}
+        prepare_text_for_tts(
+            "The data is here and the data is there",
+            pronunciation_rules=rules,
+            usage_counter=counter,
+        )
+        assert counter.get("data", 0) >= 1
+
+    def test_combined_heteronym_and_pronunciation(self):
+        from abogen.domain.pronunciation import (
+            compile_heteronym_sentence_rules,
+            compile_pronunciation_rules,
+        )
+
+        heteronym_overrides = [
+            {
+                "token": "lead",
+                "pronunciation": "led",
+                "context": "metal",
+            }
+        ]
+        pronunciation_overrides = [
+            {
+                "token": "gif",
+                "pronunciation": "jif",
+                "normalized": "gif",
+            }
+        ]
+        h_rules = compile_heteronym_sentence_rules(heteronym_overrides)
+        p_rules = compile_pronunciation_rules(pronunciation_overrides)
+
+        result = prepare_text_for_tts(
+            "A lead gif",
+            heteronym_rules=h_rules if h_rules else None,
+            pronunciation_rules=p_rules,
+        )
+        assert isinstance(result, str)
+
+    @patch("abogen.domain.normalization.get_runtime_settings")
+    def test_normalization_overrides_passed_through(self, mock_settings):
+        mock_settings.return_value = {
+            "normalization_apostrophe_mode": "spacy",
+            "normalization_enabled": True,
+        }
+        result = prepare_text_for_tts(
+            "It's a test",
+            normalization_overrides={"normalization_enabled": False},
+        )
+        assert isinstance(result, str)
+
+    def test_pronunciation_rules_empty(self):
+        result = prepare_text_for_tts("Hello", pronunciation_rules=[])
+        assert isinstance(result, str)
+
+    def test_heteronym_rules_empty(self):
+        result = prepare_text_for_tts("Hello", heteronym_rules=[])
+        assert isinstance(result, str)
+
+
+class TestNormalizeTextForPipeline:
+    """Tests for the simpler normalization function."""
+
+    def test_basic_normalization(self):
+        result = normalize_text_for_pipeline("It's a test")
+        assert isinstance(result, str)
+        assert len(result) > 0
+
+    def test_empty_text(self):
+        result = normalize_text_for_pipeline("")
+        assert result == ""
+
+    @patch("abogen.domain.normalization.get_runtime_settings")
+    def test_with_overrides(self, mock_settings):
+        mock_settings.return_value = {
+            "normalization_apostrophe_mode": "spacy",
+        }
+        result = normalize_text_for_pipeline(
+            "It's a test",
+            normalization_overrides={"normalization_apostrophe_mode": "spacy"},
+        )
+        assert isinstance(result, str)