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>

.npmignore

@@ -0,0 +1,28 @@
+# === Mirrors .gitignore — items below this block are also excluded from
+#     the npm tarball. Kept here verbatim so npm pack doesn't fall back to
+#     the .gitignore inheritance (silent + surprising). ===
+node_modules/
+package-lock.json
+*.tgz
+.env
+.env.*
+.DS_Store
+npm-debug.log*
+
+# === Dev-only content the npm tarball doesn't need ===
+# Tests + their harness — consumers load index.js, not the test tree.
+test/
+*.test.js
+
+# Wiki / docs — useful in the repo, big in the pack.
+wiki/
+
+# One-off maintenance tooling (wiki generator, etc.) not used at runtime.
+scripts/
+
+# Project memory + IDE configs.
+.claude/
+.codex/
+.repo-mem/
+CLAUDE.md
+CLAUDE.local.md