Wire doc/scanner notebooks into the integration notebook harness

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## Problem

The `doc/scanner/` notebooks (`1_pyrit_scan.ipynb`, `airt.ipynb`, `benchmark.ipynb`, `foundry.ipynb`, `garak.ipynb`) are listed in `doc/myst.yml` and render in our docs site, but nothing in CI actually executes them. The integration notebook harness (`tests/integration//test_notebooks_*.py`) is hard-coded to `doc/code//` via `pyrit.common.path.DOCS_CODE_PATH`, so the scanner notebooks are render-only.

This means breakages in the user-facing scanner API surface — like the deprecated-type slip-through fixed in #1746 — won't be caught by CI.

## Proposal

Add `tests/integration/scanner/test_notebooks_scanner.py`, mirroring the existing per-area pattern (e.g. `tests/integration/scenarios/test_notebooks_scenarios.py`). It would parametrize over `os.listdir(DOC_ROOT / "scanner")` and run each notebook via `ExecutePreprocessor` under `RUN_ALL_TESTS=true`.

Points to confirm during implementation:
- The scanner notebooks call `pyrit_scan` end-to-end with `OpenAIChatTarget()` against real datasets. They are likely slow enough to warrant `max_dataset_size=1` shims or a `skipped_files` entry for the heavy ones — pick the right cost/coverage tradeoff up front.
- `DOCS_CODE_PATH` is `doc/code` by name; introducing a parallel `DOCS_SCANNER_PATH` constant in `pyrit/common/path.py` keeps the pattern consistent.

## Context

Surfaced in the PR review thread on #1746: https://github.com/microsoft/PyRIT/pull/1746#issuecomment-4478807681

Start with tests/integration/scenarios/test_notebooks_scenarios.py, pyrit.common.path.DOCS_CODE_PATH, and the notebooks under doc/scanner/. Compare the existing per-area harness and determine how max_dataset_size=1 or skipped_files should handle the slow notebooks. Done means the scanner notebooks execute under RUN_ALL_TESTS=true and their user-facing API paths are covered by CI.

Written by the indexing model from the issue text.