feat: --color CLI flag for session color

Feature Request

Add --color and --title CLI flags to set the session color and TUI input box label at launch time.

Current behavior

• /color <color> — sets the session color in the TUI, interactive only
• /rename <name> — sets the label shown in the TUI input box, interactive only
• --name — exists but only affects session history/list, does not render in the TUI input box

Desired behavior

claude --color orange --title Mercury

• --color sets the session color (matching /color behavior)
• --title renders in the TUI input box (matching /rename behavior)

If --name can be updated to also render in the TUI input box like /rename, that works too — otherwise a separate --title flag avoids breaking the existing --name semantics.

Available colors: red, blue, green, yellow, purple, orange, pink, cyan, default

Use case

Multi-agent orchestration setups (e.g. parallel git worktrees, each running a separate Claude Code agent) want to visually distinguish sessions by color and label at launch time — without requiring interactive input after the session starts.