* docs: move entity labels detail to memory-banks, simplify retain overview
* docs: move entity labels blurb under entity-recognition section in retain
* docs: update metadata filtering FAQ to cover entity graph retrieval and entity labels tag option
* docs: enable TOC and fix missing separators in FAQ
* docs: add benchmarks leaderboard screenshot and link to models page
* docs: add 'Which model should I use?' FAQ entry with leaderboard screenshot
* docs: fix leaderboard description to cover retain, reflect, and observations