Stock Ticker Mobile: Achievements + Profile Tabs

The Android client for Stock Ticker got a big UI pass. We now have:

• Tabbed layout: Profile | Achievements.
• Locked achievements show in grayscale with a progress bar instead of just hiding.
• Stats now match the dark dashboard look from web, including streak records.

The app pulls live achievement data from the backend via Socket.IO and REST. We'll eventually sync with Google Play Games Services so we can get unlocks natively on Android devices too.

Also starting to track more stats server-side (cumulative dividends earned, most traded stock, etc.) so we can reward specific playstyles instead of only raw profit.