feat: overhaul stats dashboard with navigation, trends, and anime views

Add navigation state machine for tab/detail routing, anime overview
stats with Yomitan lookup rates, session word count accuracy fixes,
vocabulary tab hook order fix, simplified trends data fetching from
backend-aggregated endpoints, and improved session detail charts.

stats/src/lib/stats-navigation.ts

@@ -0,0 +1,139 @@
+import type { SessionSummary } from '../types/stats';
+import type { TabId } from '../components/layout/TabBar';
+
+export type MediaDetailOrigin = { type: 'anime'; animeId: number } | { type: 'overview' };
+
+export interface MediaDetailState {
+  videoId: number;
+  initialSessionId: number | null;
+  origin: MediaDetailOrigin;
+}
+
+export interface StatsViewState {
+  activeTab: TabId;
+  selectedAnimeId: number | null;
+  focusedSessionId: number | null;
+  mediaDetail: MediaDetailState | null;
+}
+
+export function createInitialStatsView(): StatsViewState {
+  return {
+    activeTab: 'overview',
+    selectedAnimeId: null,
+    focusedSessionId: null,
+    mediaDetail: null,
+  };
+}
+
+export function switchTab(state: StatsViewState, tabId: TabId): StatsViewState {
+  return {
+    activeTab: tabId,
+    selectedAnimeId: null,
+    focusedSessionId: tabId === 'sessions' ? state.focusedSessionId : null,
+    mediaDetail: null,
+  };
+}
+
+export function navigateToAnime(state: StatsViewState, animeId: number): StatsViewState {
+  return {
+    ...state,
+    activeTab: 'anime',
+    selectedAnimeId: animeId,
+    mediaDetail: null,
+  };
+}
+
+export function navigateToSession(state: StatsViewState, sessionId: number): StatsViewState {
+  return {
+    ...state,
+    activeTab: 'sessions',
+    focusedSessionId: sessionId,
+    mediaDetail: null,
+  };
+}
+
+export function openAnimeEpisodeDetail(
+  state: StatsViewState,
+  animeId: number,
+  videoId: number,
+  sessionId: number | null = null,
+): StatsViewState {
+  return {
+    activeTab: 'anime',
+    selectedAnimeId: animeId,
+    focusedSessionId: null,
+    mediaDetail: {
+      videoId,
+      initialSessionId: sessionId,
+      origin: {
+        type: 'anime',
+        animeId,
+      },
+    },
+  };
+}
+
+export function openOverviewMediaDetail(
+  state: StatsViewState,
+  videoId: number,
+  sessionId: number | null = null,
+): StatsViewState {
+  return {
+    activeTab: 'overview',
+    selectedAnimeId: null,
+    focusedSessionId: null,
+    mediaDetail: {
+      videoId,
+      initialSessionId: sessionId,
+      origin: {
+        type: 'overview',
+      },
+    },
+  };
+}
+
+export function closeMediaDetail(state: StatsViewState): StatsViewState {
+  if (!state.mediaDetail) {
+    return state;
+  }
+
+  if (state.mediaDetail.origin.type === 'overview') {
+    return {
+      activeTab: 'overview',
+      selectedAnimeId: null,
+      focusedSessionId: null,
+      mediaDetail: null,
+    };
+  }
+
+  return {
+    activeTab: 'anime',
+    selectedAnimeId: state.mediaDetail.origin.animeId,
+    focusedSessionId: null,
+    mediaDetail: null,
+  };
+}
+
+export function getSessionNavigationTarget(session: Pick<SessionSummary, 'sessionId' | 'videoId'>):
+  | {
+      type: 'media-detail';
+      videoId: number;
+      sessionId: number;
+    }
+  | {
+      type: 'session';
+      sessionId: number;
+    } {
+  if (session.videoId != null) {
+    return {
+      type: 'media-detail',
+      videoId: session.videoId,
+      sessionId: session.sessionId,
+    };
+  }
+
+  return {
+    type: 'session',
+    sessionId: session.sessionId,
+  };
+}