Stop committing pdm.lock — wlsqm is a library

Aligns wlsqm with the project-wide lockfile policy in
~/.claude/PROJECT-SETUP-NOTES.md ("Lockfile policy" section). wlsqm is a
library, not an app: downstream users install it as a dependency in
their own environment and never see our lockfile, and CI should
fresh-resolve every run against the declared dependency floors in
pyproject.toml. Committing pdm.lock would hide exactly the kind of
upstream breakage we want to catch early — e.g. a new scipy release
that silently breaks our cython_lapack cimports.

Removes pdm.lock from the index (local file kept) and adds it to
.gitignore with a pointer to the policy rationale. Contributors can
still regenerate it locally via `pdm install` for their own
reproducible dev environment; it just won't be part of the repo.

Fleet classification (per ~/.claude/PROJECT-SETUP-NOTES.md fleet table):
  - Library (no lockfile): pylu, pydgq, mcpyrate, unpythonic, wlsqm
  - App (commit lockfile): pyan3, arxiv-api-search, raven

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Technologicat

.gitignore

@@ -10,6 +10,10 @@ dist/
 *.egg-info/
 .pdm-build/
 .pdm-python
+# Library, not app — see `~/.claude/PROJECT-SETUP-NOTES.md` under "Lockfile policy".
+# CI and downstream users fresh-resolve against pyproject.toml's declared floors;
+# committing pdm.lock would hide upstream breakage we want to see early.
+pdm.lock
 .python-version
 .venv/
 .spyproject/