feat(setDemand): surface specificClass.setDemand(value, unit='%') + slim npm pack

Why:
- pumpingStation level-based control was calling MGC.handleInput(percent)
  directly. handleInput expects canonical m³/s; a 1 % keep-alive arrived
  as 1 m³/s ≈ 3600 m³/h, the dispatcher clamped to dt.flow.max and the
  group ran at 100 %. The unit math already existed inside the set.demand
  command handler — but only that handler could reach it.

What:
- New public method `async setDemand(value, unit='%')` on MachineGroup
  (specificClass.js). Resolves the unit (`%` → interpolate against the
  dynamic-totals envelope, absolute units → convert(value)) and calls
  handleInput with canonical m³/s. Negative value remains the operator
  stop-all signal. Single source of truth for the percent → m³/s rule.
- Refactor handlers.setDemand to parse the payload + apply mode gating
  and then delegate to source.setDemand. Drops the local `convert` import
  (now reached via the source).
- Update commands.basic.test.js mock with a setDemand shim that mirrors
  the real method, so existing handleInput assertions still hold.

Packaging:
- Add .npmignore mirroring .gitignore plus dev-only trees (test/, wiki/,
  CLAUDE.md, …) so the published tarball stays small.
- Extend .gitignore with the standard dev-artifact deny list.

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*
+
+# Large local screen recording (>100 MB) — kept out of both repo and pack.
+wiki/test.gif
+
+# === Dev-only content the npm tarball doesn't need ===
+# Tests + their harness — Node-RED loads the entry .js, not the test tree.
+test/
+*.test.js
+
+# Wiki / docs — useful in the repo, big in the pack.
+wiki/
+
+# Project memory + IDE configs.
+.claude/
+.codex/
+.repo-mem/
+CLAUDE.md
+CLAUDE.local.md