feat: adopt pairwise-tests (PICT combinatorial) + cross-reference from existing testing skills

Forked verbatim from omkamal/pypict-claude-skill (MIT). LICENSE preserved.
Renamed from `pict-test-designer` to `pairwise-tests` — technique-first
naming so users invoking "pairwise" or "combinatorial" find it; PICT
remains the tool under the hood.

Bundle (skill-runtime only):
  pairwise-tests/SKILL.md                    (renamed, description rewritten)
  pairwise-tests/LICENSE                     (MIT, preserved)
  pairwise-tests/references/pict_syntax.md
  pairwise-tests/references/examples.md
  pairwise-tests/scripts/pict_helper.py      (Python CLI for model gen / output fmt)
  pairwise-tests/scripts/README.md

Upstream's repo-level docs (README, QUICKSTART, CONTRIBUTING, etc.) and
`examples/` dir (ATM + gearbox walkthroughs — useful as reading, not as
skill-runtime) omitted from the fork. Attribution footer added.

Cross-references so /add-tests naturally routes to /pairwise-tests when
warranted:

- add-tests/SKILL.md Phase 2 step 8: if a function in scope has 3+ parameters
  each taking multiple values, surface `/pairwise-tests` to the user before
  proposing normal category coverage. Default continues with /add-tests;
  user picks pairwise explicitly.
- claude-rules/testing.md: new "Combinatorial Coverage" section after the
  Normal/Boundary/Error categories. Explains when pairwise wins, when to
  skip (regulated / provably exhaustive contexts, ≤2 parameters, non-
  parametric testing), and points at /pairwise-tests.
- languages/python/claude/rules/python-testing.md: new "Pairwise /
  Combinatorial for Parameter-Heavy Functions" subsection under the
  parametrize guidance. Explains the pytest workflow: /pairwise-tests
  generates the matrix, paste into pytest parametrize block, or use
  pypict helper directly.

Mechanism note: cross-references are judgment-based — Claude reads the
nudges in add-tests/testing/python-testing and acts on them when appropriate,
not automatic dispatch. Craig can still invoke /pairwise-tests directly when
he already knows he wants combinatorial coverage.

Makefile SKILLS extended; make install symlinks /pairwise-tests globally.

1 files changed, 35 insertions, 0 deletions

diff --git a/pairwise-tests/LICENSE b/pairwise-tests/LICENSE
new file mode 100644
index 0000000..e40dc44
--- /dev/null
+++ b/pairwise-tests/LICENSE
@@ -0,0 +1,35 @@
+MIT License
+
+Copyright (c) 2025 pypict-claude-skill contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+---
+
+This project uses and acknowledges the following tools:
+
+PICT (Pairwise Independent Combinatorial Testing)
+Copyright (c) Microsoft Corporation
+Licensed under the MIT License
+https://github.com/microsoft/pict
+
+pypict - Python binding for PICT
+Copyright (c) Kenichi Maehashi
+Licensed under the MIT License
+https://github.com/kmaehashi/pypict