feat: Polar license key integration and dashboard UI improvements

- Add license activation flow: server validates/activates keys via Polar SDK
- Auto-activate from Polar checkout redirect (checkout_id in URL)
- Gate dashboard behind license activation (redirect to /activate if no plan)
- Preserve redirect URL through login flow for post-purchase activation
- Show plan status badge in sidebar and overview page
- Add account section to settings (email, plan, license key)
- Add svelte-sonner toasts with custom black theme and iconify icons
- Improve validation messages across all forms
- Update API key prefix to droidclaw_
- Add cursor pointer globally for clickable elements
- Support Polar sandbox mode via POLAR_SANDBOX env flag

web/src/lib/api/api-keys.remote.ts

@@ -10,7 +10,7 @@ export const listKeys = query(async () => {
 export const createKey = form(createKeySchema, async ({ name }) => {
 	const { request } = getRequestEvent();
 	const result = await auth.api.createApiKey({
-		body: { name, prefix: 'dc' },
+		body: { name, prefix: 'droidclaw_' },
 		headers: request.headers
 	});
 	return result;