/export (TUI) and opencode export (CLI) are unrelated commands with the same name — causes silent-looking import failures

Description

/export in the TUI and opencode export on the CLI share a name but do completely different things:

Nothing about /export indicates it's not the counterpart to opencode import. A user trying to hand a session to a colleague to continue naturally reaches for /export (it's discoverable in the TUI; the CLI command isn't visible unless you already know to look for it), gets a .md file, and only discovers it's the wrong format when opencode import rejects it.

Steps to reproduce

1. In the TUI, run /export on a session → get session.md.
2. opencode import session.md
3. Import fails (not valid JSON).

Suggested fixes (any one of these would help; happy to see other approaches)

• Rename /export to something that doesn't imply session-portability, e.g. /transcript or /export-md.
• Or, have opencode import detect a Markdown/non-JSON file and fail with a specific message pointing at opencode export instead of a generic parse error.
• Or, document the distinction inline — e.g. /export's TUI description could say "for reading only; use opencode export/opencode import to transfer a session."

Why it matters

Right now the only way to learn these are unrelated is to hit the failure and go read the CLI docs page separately from the TUI docs page — there's no signal at the point of using either command.