feat(cli): add --prompt-interactive to seed an initial prompt without leaving the interactive session

Today kimi -p "..." runs once and exits; there is no way to hand Kimi an initial prompt while keeping the interactive session alive.

Motivation: agent-to-agent handoffs. Persistent multi-agent setups increasingly launch one agent CLI from another and keep it alive for ongoing interaction. Other agent CLIs support this directly — claude "prompt" and codex "prompt" accept an initial prompt and keep the REPL open, and opencode --prompt "..." seeds the TUI with an initial prompt on launch. Kimi is the outlier: an orchestrator must spawn kimi, watch the pane to detect that startup completed, and only then inject the first prompt as a second step. A single flag turns that dance into one command:

kimi --prompt-interactive "Summarize today's changes and wait for further instructions"

Proposal. Add -P / --prompt-interactive <text>: after startup completes, submit the value through the normal input pipeline and keep the session open. The value can be a plain prompt or a slash command (e.g. seeding a session with /init or a skill trigger). Behavior notes:

• mutually exclusive with -p/--prompt; empty values rejected
• composable with --yolo, --plan, --continue, and --session <id>
• no behavior change for existing invocations

Other use cases. Shell aliases that pre-seed a review prompt; IDE/editor integration that opens Kimi with the current file or selection as context; starting a session with a complex multi-line prompt without pasting it after launch.

Additional information

• I previously ported this to kimi-code as PR #23, which was closed pending prior discussion — hence this issue first.
• I have a working implementation of the above (including the engineV2 session-less startup path) and can open a PR promptly if the feature is accepted.

Start at the CLI option entry point and normal input pipeline, then trace the engineV2 session-less startup path. Compare existing -p/--prompt handling with the requested flag and its listed option combinations; done means the initial prompt or slash command is submitted after startup while the session remains open, without changing existing invocations.