feat: tag codex harness on signup + plugin-setup prompt

[dimavrem22]

What

Two small changes:

1. Signup attribution — pass harness="codex" as a keyword to the Inkbox.signup(...) call in inkbox_codex/setup_wizard.py so agents that self-sign-up from this harness are tagged accordingly.
2. Plugin-permission prompt — add a short note to CHANNEL_PROMPT (inkbox_codex/prompts.py) telling the agent that if it self-signed-up to Inkbox without this plugin configured, it should ask the human for permission before setting up the plugin, since the plugin wires native messaging channels directly into its runtime.

Dependency

The harness keyword depends on the Inkbox Python SDK gaining a harness parameter on Inkbox.signup(...). This PR should land alongside / after that SDK change.

Related PRs (agent-signup harness)

• feat: add harness param to agent signup (SDK + CLI + skill) inkbox#79 — SDK (py/ts) + CLI + self-signup skill (adds the harness param this builds on)
• feat: tag claude-code harness on signup + plugin-setup prompt claude-code-plugin#17
• feat: tag codex harness on signup + plugin-setup prompt #5
• feat: tag openclaw harness on signup + plugin-setup skill openclaw-plugin#20
• feat: tag hermes harness on signup + plugin-setup skill hermes-agent-plugin#19

[dimavrem22]

codex: This now passes harness="codex" into Inkbox.signup, but the plugin still declares/installs inkbox>=0.4.7, and _ensure_inkbox_sdk() returns immediately when any older SDK imports successfully. Since the harness keyword is introduced by the SDK PR (0.4.9), existing environments with inkbox==0.4.7 can raise TypeError before the request reaches the server. Please bump the dependency/bootstrap minimum to the SDK version that supports harness, or feature-detect the signup signature and fall back cleanly.

[dimavrem22]

Fixed in f7ab3b0: bumped inkbox>=0.4.7 → >=0.4.9 (pyproject, INKBOX_REQUIREMENTS, hints, requirement-string tests) and added a MIN_INKBOX_VERSION guard in _ensure_inkbox_sdk() so an importable-but-stale (<0.4.9) SDK is treated as missing and upgraded via the existing install path before the harness= call.

[dimavrem22]

Correction: the harness-capable SDK release is 0.4.10, not 0.4.9. Pins, INKBOX_REQUIREMENTS, the min-version guard, hints, and tests are now all 0.4.10 (c65fd5b).