feat(pumpingStation schema): add holdLevel + deadZoneKeepAlivePercent; slim npm pack

Schema:
- holdLevel (optional, default null → equals startLevel): 0 % ramp foot for
  the levelbased curve. When raised above startLevel, pumps engage at
  startLevel but hold at MGC flow.min across [startLevel, holdLevel] before
  the ramp begins.
- deadZoneKeepAlivePercent (default 1): percent emitted across the
  [stopLevel, startLevel] falling-edge keep-alive band.
- Refreshed startLevel / stopLevel descriptions: hysteresis is no longer
  coupled to inflowLevel (was misleading).

Packaging:
- Add .npmignore mirroring .gitignore plus the dev-only trees (test/,
  wiki/, scripts/, .claude/, …) so npm pack doesn't ship the doc set.
- Extend .gitignore with the standard dev-artifact deny list so both
  files share the same baseline.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,5 +1,14 @@
+# Repo dev artifacts. Mirrors the deny list in .npmignore so the two stay
+# in sync — anything that shouldn't be committed AND shouldn't ship in the
+# npm tarball goes in both files.
 node_modules/
 
 # Local stub generated by `npm install` in the submodule directory.
 # generalFunctions has no production deps of its own.
 package-lock.json
+
+*.tgz
+.env
+.env.*
+.DS_Store
+npm-debug.log*