feat: add Home page with user dashboard and habit tracking features

- Implemented Home component with user authentication and loading states.
- Created Welcome component for unauthenticated users with a sign-in option.
- Developed Dashboard component to display user's habits and progress.
- Added functionality for habit management, including adding, updating, and deleting habits.
- Integrated HabitChart and HabitHistory components for visual representation of habits.
- Introduced sharing functionality for progress via Discord integration.

feat: establish Discord sharing configuration and routes

- Added DiscordSharingConfig type and readDiscordSharingConfig function for environment variable management.
- Created sharing contracts for input validation and data structure.
- Implemented sharing routes for previewing and sending progress images to Discord.
- Added tests for sharing routes to ensure authentication and proper error handling.

src/sharing/config.ts

@@ -0,0 +1,9 @@
+export type DiscordSharingConfig = { token: string; channelId: string };
+
+/** Read only from the server entrypoint; never include credentials in public config. */
+export function readDiscordSharingConfig(env = process.env): DiscordSharingConfig {
+  return {
+    token: (env.DISCORD_BOT_TOKEN ?? "").trim().replace(/^Bot\s+/i, ""),
+    channelId: (env.DISCORD_SHARING_CHANNEL_ID ?? "").trim(),
+  };
+}