feat: add theme provider and control components for light/dark mode

- Implemented ThemeProvider to manage theme state and preferences.
- Added ThemeControl component for users to switch between system, light, and dark themes.
- Integrated localStorage for theme preference persistence.
- Updated document styles based on theme changes.

test: add tests for permanent deletion of habits and related records

- Created tests to ensure permanent deletion of habits removes all dependent records.
- Verified that deletion requires ownership, authentication, and checks for archived habits.
- Added tests to confirm rollback behavior on deletion failures.

test: add tests for habit palette and progress card functionality

- Implemented tests for habit color progression and theme-based color shading.
- Added tests for progress card calculations and calendar display logic.

feat: define theme types and preferences

- Introduced Theme and ThemePreference types for better type safety.
- Created utility functions for resolving theme based on user preference and system settings.
- Defined theme palettes for light and dark modes to ensure adequate contrast.

src/components/AccountSettings.tsx

@@ -1,3 +1,4 @@
+import { ThemeControl } from "./ThemeProvider";
 import { ReminderSettings } from "./ReminderSettings";
 import { useId, useRef, useState } from "react";
 import type { PublicUser } from "../shared/user";
@@ -24,6 +25,7 @@ export function AccountSettings({ user, onChanged, onClose }: { user: PublicUser
     finally { saving.current = false; setBusy(false); }
   }
   return <WorkspacePanel id="account-settings" eyebrow="YOUR WORKSPACE" title="Account settings" description="A few preferences to make this space yours." onClose={onClose} busy={busy || reminderBusy} closeLabel="Close settings">
+    <SettingRow title="Appearance" description={<p>Follow your device or choose a theme for this browser.</p>}><ThemeControl /></SettingRow>
     <SettingRow title="Your daily rhythm" description={<p>Your timezone sets the start and end of each day. Earlier deadlines stay as recorded.</p>}>
       <form className="ds-form-stack" onSubmit={event => { event.preventDefault(); void run(() => habitRequest("/me", { method: "PATCH", headers: { "Content-Type": "application/json" }, body: JSON.stringify({ timezone }) })); }}>
         <Field label="Timezone">
@@ -35,7 +37,7 @@ export function AccountSettings({ user, onChanged, onClose }: { user: PublicUser
     </SettingRow>
     <ReminderSettings timezone={user.timezone} onBusyChange={setReminderBusy} disabled={busy} />
     <SettingRow title="A copy for you" description={<p>Take your profile, habits, history, and sharing records with you. Sessions and credentials are excluded.</p>}>
-      <div className="ds-action-row"><ButtonLink variant="secondary" href="/api/account/export" download="minabot-export.json"><Download size={16} aria-hidden="true" />Export my data</ButtonLink><span className="ds-meta-label">JSON file</span></div>
+      <div className="ds-action-row"><ButtonLink variant="secondary" href="/api/account/export" download="mina-habits-export.json"><Download size={16} aria-hidden="true" />Export my data</ButtonLink><span className="ds-meta-label">JSON file</span></div>
     </SettingRow>
     <SettingRow title="Delete account" description={<p>Permanently remove your account and habit history, and sign out every device.</p>}>
       {!deleting ? <div className="ds-action-row"><Button variant="text" disabled={busy || reminderBusy} onClick={() => setDeleting(true)} aria-expanded={false}><Trash2 size={16} aria-hidden="true" />Delete account</Button></div> :