feat(immersion): add anime metadata, occurrence tracking, and schema upgrades

- Add imm_anime table with AniList integration
- Add imm_subtitle_lines, imm_word_line_occurrences, imm_kanji_line_occurrences
- Add POS fields (part_of_speech, pos1, pos2, pos3) to imm_words
- Add anime metadata parsing with guessit fallback
- Add video duration tracking and watched status
- Add episode, streak, trend, and word/kanji detail queries
- Deduplicate subtitle line recording within sessions
- Pass Anki note IDs through card mining callback chain

src/core/services/immersion-tracker/legacy-vocabulary-pos.ts

@@ -0,0 +1,71 @@
+import type { Token } from '../../../types';
+import type { LegacyVocabularyPosResolution } from './types';
+import { deriveStoredPartOfSpeech } from '../tokenizer/part-of-speech';
+
+const KATAKANA_TO_HIRAGANA_OFFSET = 0x60;
+const KATAKANA_CODEPOINT_START = 0x30a1;
+const KATAKANA_CODEPOINT_END = 0x30f6;
+
+function normalizeLookupText(value: string | null | undefined): string {
+  return typeof value === 'string' ? value.trim() : '';
+}
+
+function katakanaToHiragana(text: string): string {
+  let normalized = '';
+  for (const char of text) {
+    const code = char.codePointAt(0);
+    if (code === undefined) {
+      continue;
+    }
+    if (code >= KATAKANA_CODEPOINT_START && code <= KATAKANA_CODEPOINT_END) {
+      normalized += String.fromCodePoint(code - KATAKANA_TO_HIRAGANA_OFFSET);
+      continue;
+    }
+    normalized += char;
+  }
+  return normalized;
+}
+
+function toResolution(token: Token): LegacyVocabularyPosResolution {
+  return {
+    headword: normalizeLookupText(token.headword) || normalizeLookupText(token.word),
+    reading: katakanaToHiragana(normalizeLookupText(token.katakanaReading)),
+    partOfSpeech: deriveStoredPartOfSpeech({
+      partOfSpeech: token.partOfSpeech,
+      pos1: token.pos1,
+    }),
+    pos1: normalizeLookupText(token.pos1),
+    pos2: normalizeLookupText(token.pos2),
+    pos3: normalizeLookupText(token.pos3),
+  };
+}
+
+export function resolveLegacyVocabularyPosFromTokens(
+  lookupText: string,
+  tokens: Token[] | null,
+): LegacyVocabularyPosResolution | null {
+  const normalizedLookup = normalizeLookupText(lookupText);
+  if (!normalizedLookup || !tokens || tokens.length === 0) {
+    return null;
+  }
+
+  const exactSurfaceMatches = tokens.filter(
+    (token) => normalizeLookupText(token.word) === normalizedLookup,
+  );
+  if (exactSurfaceMatches.length === 1) {
+    return toResolution(exactSurfaceMatches[0]!);
+  }
+
+  const exactHeadwordMatches = tokens.filter(
+    (token) => normalizeLookupText(token.headword) === normalizedLookup,
+  );
+  if (exactHeadwordMatches.length === 1) {
+    return toResolution(exactHeadwordMatches[0]!);
+  }
+
+  if (tokens.length === 1) {
+    return toResolution(tokens[0]!);
+  }
+
+  return null;
+}