Description

Adoption feature, terminal-file-manager layer (distinct from TASK-015 $EDITOR and TASK-016 OS associations). When a user hits 'open' (not 'open externally') on a .md/.txt file in a TUI file manager, route it to glint. Each manager has its own opener config, independent of $EDITOR:

• Yazi: ~/.config/yazi/yazi.toml — an [opener] entry { run = 'glint "$@"', block = true } plus [open] rules for name='.md' and mime='text/'. block=true runs glint in the foreground. Overrides Yazi's default $EDITOR opener for text only.
• ranger: rifle.conf rule (mime ^text → glint "$@").
• lf: 'cmd open' script dispatching text/markdown to glint.
• nnn: nuke/opener script entry. Ship documented snippets in the README, and optionally a glint -c step that detects an installed manager and offers to append the rule (idempotent, reversible). Keep $EDITOR untouched so code editing is unaffected.

Acceptance Criteria

• #1 README documents opener snippets for Yazi (and ranger/lf/nnn) routing text/markdown 'open' to glint
• #2 Yazi rule uses block=true and overrides only text/markdown, leaving $EDITOR alone
• #3 Optional: glint -c detects an installed file manager and offers to add the rule idempotently