v2: folder-first opening like cosmic-player (sidebar, capture sets, no portal keyholes)

Owner direction (2026-08-01, planned now, NOT for v1): pivot the primary open flow to what cosmic-player does - the user opens a FOLDER (with a sidebar listing its videos); clicking a video gives the app the whole directory, so lens mates (#123), sequential chunks (#127) and LRV siblings (#133) are always reachable, with read-only grants and zero portal keyhole cases: one folder document contains everything.

Design sketch to refine when scheduled: File > Open folder (chooser portal directory=true, one document for the tree), sidebar in cosmic-player's idiom listing captures (grouped by capture set via kjerag_meta::capture::resolve, chunks collapsed), selection plays. Single-file open stays for drags/CLI/double-click (bare paths under the ro grants).

v1 interim (shipping in #132): grants stay :ro; chooser picks of two-file captures play one lens with guidance on how to do it properly (pick both / drag from the file manager). Owner: 'This is an edge case - not a problem in v4.'