feat: Figure out Firebase composite indices

Composite indices good. Slow reads bad. Uhhhh. It's 5:15 AM as I write this. I have thoughts on this I swear. Slow reads bad, slow writes passable. We can optimistically show tags on apply/writes, but we need reads to be snappy.

No files, tests, or linked pull requests are referenced. First, locate the Firestore read/write logic for photo tags in the TypeScript codebase, then find any Firebase index configuration (or deployment config) used by the project. Identify the slow read queries and map each needed composite index to those query filters/orderings. Done when the proposed composite-index updates are in place and the intended read paths are no longer the bottleneck.

Written by the indexing model from the issue text.