feat: v0.4.0 - provider icon system, settings modal & polish

- Add provider icon system with extracted icon library (cc-switch based)

- Persist icon and icon_color in SQLite and config.toml

- Add Settings modal (theme / language / update check / silent download)

- Add useTheme and useUpdateCheck hooks

- Add provider icon picker (IconPicker) with search and grid

- Fix icon frame 2-layer color difference in ProviderEdit

- Dashboard heatmap and daily usage improvements

- Sessions page polish and adaptive layout

- Bump version to 0.4.0

src/hooks/useTheme.ts

@@ -0,0 +1,62 @@
+import { useEffect, useState } from "react";
+
+export type Theme = "light" | "dark" | "auto";
+export type ResolvedTheme = "light" | "dark";
+
+const STORAGE_KEY = "kimi-switch-theme";
+
+function getSystemTheme(): ResolvedTheme {
+  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+}
+
+function getInitialTheme(): Theme {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY) as Theme | null;
+    if (stored === "light" || stored === "dark" || stored === "auto") return stored;
+  } catch {
+    // ignore
+  }
+  return "auto";
+}
+
+function applyTheme(theme: Theme): ResolvedTheme {
+  const resolved: ResolvedTheme = theme === "auto" ? getSystemTheme() : theme;
+  const root = document.documentElement;
+  root.classList.toggle("dark", resolved === "dark");
+  root.classList.toggle("light", resolved === "light");
+  return resolved;
+}
+
+export function useTheme() {
+  const [theme, setThemeState] = useState<Theme>(getInitialTheme);
+  const [resolvedTheme, setResolvedTheme] = useState<ResolvedTheme>(() => applyTheme(getInitialTheme()));
+
+  // Apply theme on change
+  useEffect(() => {
+    const resolved = applyTheme(theme);
+    setResolvedTheme(resolved);
+  }, [theme]);
+
+  // Listen to system theme changes when in "auto" mode
+  useEffect(() => {
+    if (theme !== "auto") return;
+    const media = window.matchMedia("(prefers-color-scheme: dark)");
+    const handler = () => {
+      const resolved = applyTheme("auto");
+      setResolvedTheme(resolved);
+    };
+    media.addEventListener("change", handler);
+    return () => media.removeEventListener("change", handler);
+  }, [theme]);
+
+  const setTheme = (next: Theme) => {
+    setThemeState(next);
+    try {
+      localStorage.setItem(STORAGE_KEY, next);
+    } catch {
+      // ignore
+    }
+  };
+
+  return { theme, resolvedTheme, setTheme };
+}

src/hooks/useUpdateCheck.ts

@@ -0,0 +1,58 @@
+import { useCallback, useEffect, useState } from "react";
+import { invoke } from "@tauri-apps/api/core";
+
+export interface UpdateInfo {
+  current: string;
+  latest: string;
+  updateAvailable: boolean;
+  releaseUrl: string;
+  downloadUrl: string | null;
+}
+
+const THROTTLE_KEY = "kimi-switch-last-update-check";
+const THROTTLE_MS = 24 * 60 * 60 * 1000; // 24 hours
+
+export function useUpdateCheck() {
+  const [updateInfo, setUpdateInfo] = useState<UpdateInfo | null>(null);
+  const [checking, setChecking] = useState(false);
+  const [lastChecked, setLastChecked] = useState<number | null>(() => {
+    try {
+      const v = localStorage.getItem(THROTTLE_KEY);
+      return v ? Number(v) : null;
+    } catch {
+      return null;
+    }
+  });
+
+  const doCheck = useCallback(async (force: boolean) => {
+    if (!force) {
+      if (lastChecked && Date.now() - lastChecked < THROTTLE_MS) return;
+    }
+    setChecking(true);
+    try {
+      const info = await invoke<UpdateInfo>("check_for_update");
+      setUpdateInfo(info);
+      const now = Date.now();
+      setLastChecked(now);
+      try {
+        localStorage.setItem(THROTTLE_KEY, String(now));
+      } catch {
+        // ignore
+      }
+    } catch {
+      // silently fail — user can retry from Settings
+    } finally {
+      setChecking(false);
+    }
+  }, [lastChecked]);
+
+  // On mount: throttled auto-check
+  useEffect(() => {
+    doCheck(false);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  const checkNow = useCallback(() => doCheck(true), [doCheck]);
+
+  return { updateInfo, checking, checkNow, lastChecked };
+}