Add --init-commands flag to execute slash commands at session startup

Problem

When launching an interactive session, there's no way to pre-execute slash commands like /rename, /color, /model, etc. Users who want a named/coloured session have to launch claude, wait for the TUI, then manually type the commands.

The existing -n / --name flag sets the session's internal name but doesn't trigger the visual prompt-bar tag and colour that /rename produces — so even that partial workaround isn't equivalent.

Proposed solution

Add an --init-commands (or similar) flag that accepts one or more slash commands to run before the first user turn:

claude --init-commands "/rename auth-refactor" "/color blue"

Alternatively/additionally, make -n/--name also trigger the visual tag/colour behaviour that /rename does, for parity.

Why this matters

• Scripted/templated launches (wrapper shell functions, project-specific aliases)
• tmux/iTerm session layouts that launch multiple pre-configured Claude instances
• Reproducible session setup across team members

Related

• #47679 — requests programmatic access to /rename and /color from tools/skills (runtime angle; this issue covers the CLI launch angle)