Badge, colored help and short errors in the ViraStack AI CLI

• Title: init and remove start with a "ViraStack AI" badge on the accent color ViraStack Start uses, with the version dimmed next to it.
• --help: Headings are bold, commands and flags use the accent color. The text and its layout stay the same.
• Errors: An error starts with a red ✖. A long message keeps its first line and at most its last 8 lines, dimmed.
• When colors show: Only in an interactive terminal. A non-empty NO_COLOR turns them off; FORCE_COLOR turns them on, and 0 or false turns them off. Pipes, CI logs and the ViraStack Start setup get plain text.

• Same look as Start: The ViraStack Start CLI got a badge, colored help and short errors, while the AI CLI still printed plain text, so the two looked like different products.
• No dependency: The colors are a few ANSI codes, so @virastack/ai still has no runtime dependencies.
• Limits: We checked the output with tests and on macOS. We did not try Windows terminals or light terminal themes.

• NO_COLOR: disabling ANSI color output by default

Nothing to do. The text of the output is the same; only its colors changed, and errors now start with ✖. A script that matches an error message exactly should allow the ✖ prefix.