docs: tighten v1.12.0 highlights to flagship features

Drop three lower-impact items from the Highlights list (still documented
in the body): audio visualizer (author notes minimal visibility), LaTeX
math (niche), and pinned DMs (minor QoL). Keeps the headline payment,
privacy, and new-feed features front and center.

https://claude.ai/code/session_01Y8cDkDRV48GYdQd3CR4kuV

docs/changelog/v1.12.00.md

@@ -6,13 +6,10 @@ Highlights:
 - **CLINK payments** — a new Lightning rail with budgets and a unified Send Payment screen.
 - **Private posts & reactions** — post, reply, react, and zap privately via NIP-17.
 - **Workouts** — record and browse NIP-101e workouts in a dedicated feed.
-- **Math in notes** — write inline and block LaTeX in the timeline.
-- **Audio visualizer** — a live, styleable visualizer for audio-only notes.
 - **Activity cards** — likes, zaps, and nutzaps render as rich gradient cards.
 - **Software Apps** — a browsable NIP-82 app directory.
 - **Music** — publish and browse music tracks and playlists.
 - **Podcasts** — a new NIP-F4 podcast feed with favorites and an inline player.
-- **Pinned DMs** — pin conversations to the top of the chat list.
 - **Desktop** — image compression, a new media player, group DMs, and a refreshed feed.
 
 ## New Features