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>

.gitignore

@@ -1,3 +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/
+package-lock.json
+*.tgz
+.env
+.env.*
+.DS_Store
+npm-debug.log*
+
 # Large local artifacts that don't belong in Git.
 # wiki/test.gif: screen recordings of the dashboard are kept locally for
 # reference but exceed 100 MB — use Git LFS or external storage if they