[Parked until product proof] Colab notebook gallery for showcase demos

Summary

The project has exactly one notebook (notebooks/context_rot_live.ipynb)
and no zero-install way to interact with contextweaver. Because the
demos are deterministic and network-free, they are ideal Colab material:
add a small notebook gallery mirroring the four showcase scenarios, each
with an "Open in Colab" badge, linked from the README and docs.

Why this matters

• A Colab badge is the lowest-friction "try it now" path that exists —
  no install, no API keys (the demos already need none), runs on any
  laptop or phone browser.
• Notebooks convert README visitors into users at the exact moment of
  curiosity, and give talks/workshops ready-made material.
• The existing showcase (docs/showcase.md) is currently read-only;
  notebooks make it executable.

Proposed scope

• notebooks/ gains four notebooks mirroring docs/showcase.md:
  1. Route 1,000 tools → 5 ChoiceCards (with RouteTrace inspection)
  2. Firewall a 16 KB tool result (artifact drilldown)
  3. 50-turn conversation → phase-budgeted pack (BuildStats deep dive)
  4. The 60-second failure mode (killer demo, narrated)
• Each notebook: %pip install contextweaver first cell, markdown
  narration between steps, ends with "where to go next" links.
• "Open in Colab" badges in notebooks/README.md (new), docs/showcase.md,
  and the README links row.
• CI execution check: run notebooks headlessly (e.g.
  jupyter nbconvert --execute or papermill) in the Python 3.12 cell so
  they can't drift — same philosophy as the existing demo drift gates.

Implementation notes

• Colab badge URL pattern:
  https://colab.research.google.com/github/dgenio/contextweaver/blob/main/notebooks/<name>.ipynb.
• Keep outputs stripped in git (pre-commit nbstripout or committed
  clean) to keep diffs reviewable; the execution check validates they
  still run.
• Pin nothing inside notebooks beyond contextweaver itself; they should
  exercise the released package, with a commented pip install -e . line
  for development.
• The existing context_rot_live.ipynb should join the gallery and get
  the same badge + CI treatment.

Acceptance criteria

• Four new notebooks run top-to-bottom in a fresh Colab runtime with
  no API keys.
• Badges visible in README, showcase page, and notebooks README.
• CI executes all notebooks in one matrix cell; failures gate.
• Notebook outputs stripped in version control.

Out of scope

• Hosted JupyterHub/Binder infrastructure.
• Notebooks requiring API keys or network.
• The in-browser Pyodide playground (separate proposal).

References

• Existing notebook: notebooks/context_rot_live.ipynb
• Showcase scenarios: docs/showcase.md
• Colab GitHub integration: https://colab.research.google.com/github/

Priority: P2 · Effort: S · Impact: Medium

Start with notebooks/context_rot_live.ipynb and docs/showcase.md to map the four scenarios and existing demo drift gates. Add the four gallery notebooks, badges in notebooks/README.md, docs/showcase.md, and the README links row, then run the notebooks headlessly in the Python 3.12 CI cell. Done means all notebooks run without API keys, outputs are stripped, and CI gates on execution failures.