CLI: a closed stdout ends vectorcraft-cli quietly

[japbcoelho]

What and why

vectorcraft-cli commands | head -1 panicked and exited with status 101:

thread 'main' panicked at /rustc/b940084d7eb6a299eb4bfeb8e34901bc051e7ac4/library/std/src/io/stdio.rs:1168:9:
failed printing to stdout: Broken pipe (os error 32)

println! and print! panic when stdout is closed. The CLI now prints through outln! and out!: a broken pipe ends the program with status 0, since the reader already has what it wanted, and any other write error goes to stderr with status 1. storytold/designcraft#43 makes the same change in DesignCraft.

How it was tested

closed_stdout_ends_quietly in apps/vectorcraft-cli/tests/cli.rs reads the first 16 bytes of commands, about 270 KB in all, and closes the pipe. It fails on main 2c02502 and passes with the fix.

Checklist

• cargo xtask ci passes (fmt, clippy, tests, assets, brands, layers, wasm).
• No panics in shipped code: no unwrap(), expect(), panic!, unreachable!, todo! or
  unimplemented! outside tests, and no unchecked indexing on data from files, parameters or
  messages. Errors are returned as Result and shown to the user
  (why and how).
• Clean-room: nothing copied from Adobe products or GPL/AGPL code (AGENTS.md).
• Every new asset has a row in ASSETS.md (no new assets).

🤖 Generated with Claude Code

[echelon]

Thanks @japbcoelho, merged! vectorcraft-cli commands | head ending quietly instead of panicking on a broken pipe is the right Unix behaviour, and routing every print through one place that tells a closed pipe apart from a real write error is tidy. Full CI passes with your test.

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