Fix ipython pin breaking Google Colab; update deprecated guardian_check API

[planetf1]

** Still working on this - validating on colab/local. Not ready **

Problem

Two bugs in the hello_mellea tutorial notebook:

1. ipython>=8.10.0 breaks Google Colab

The [tutorials] extra pinned ipython>=8.10.0, which upgrades Colab's tightly-pinned ipython==7.34.0 to 9.x. This breaks the google-colab package, destabilises the runtime, and causes a forced kernel restart with conflicts against gradio and google-adk.

2. Deprecated target_role parameter in guardian_check calls

hello_mellea.ipynb calls guardian_check(..., target_role="user"), which was deprecated in mellea PR #1037 (merged 2026-05-18, landed in mellea==0.6.0 — the version pinned by this project). Every run produces DeprecationWarning noise and will break when the parameter is removed.

Fix

pyproject.toml: Relax ipython>=8.10.0 → ipython>=7.0. Colab's 7.34.0 satisfies the floor so pip leaves it untouched; a fresh local environment still gets ipython installed for the IPython.display imports used in granite_switch.tutorials.

tutorials/notebooks/hello_mellea.ipynb: Replace target_role="user" with scoring_schema="user_prompt" in both guardian_check calls (direct equivalent per mellea's _TARGET_ROLE_TO_SCHEMA mapping). Also clears saved cell outputs — notebooks committed clean.

Testing

• hello_mellea.ipynb verified end-to-end in Google Colab (T4) against branch install
• rag_101.ipynb — to be tested in Colab and standalone
• rag_flow.ipynb — to be tested in Colab and standalone
• Standalone local run (all three notebooks)

The ipython fix applies to all three [tutorials] notebooks; only hello_mellea has the guardian_check deprecation.