Speed up the usage page

The usage page now loads in well under two seconds instead of over four, so billing and consumption analytics appear almost instantly.

• Improved usage analytics query speed by collapsing eight database round trips into two and adding date-range indexes
• Added instant rendering from a server-prefetched cache, removing the wait for the page to become interactive before data loads
• Improved annual billing views to show a clean monthly breakdown instead of 365 daily bars
• Fixed empty monthly and weekly charts for users in time zones ahead of UTC