feat(registry): AssetResolver + diffuser supplier curves (Jäger / Aerostrip / PIK / PRK)

Two related changes bundled together because the diffuser curve files
only make sense once the registry namespace they live in exists.

src/registry — new asset-metadata resolver:
- AssetResolver with synchronous resolve(namespace, id) + lazy cache,
  async refresh() for future remote pulls.
- FileBackend (per-id or single-file layouts, case-insensitive) and a
  stub HttpBackend (disabled unless EVOLV_ASSET_REMOTE=1).
- Namespaces: curves, menu, monsterSamples, monsterSpecs, units. Menu
  namespace re-keys by inner softwareType + filename so editors that
  pass either string resolve to the same tree.
- README explains how to add a namespace.
- AssetCategoryManager (datasets/assetData/index.js) becomes a thin
  facade over the resolver so existing consumers don't move.
- 246/246 tests pass — including the 39-test registry suite.

datasets/assetData — file moves + new diffuser data:
- modelData/*.json deleted; curves/*.json is the canonical home.
- New diffuser.json menu tree with GVA, Jäger, Aquaconsult/Entec,
  PIK/PRK suppliers.
- gva-elastox-r.json migrated from the inline _loadSpecs hardcode,
  re-tagged coverageBasis="bottom-coverage-pct" (the legacy 2.4
  elements/m² was a prior mis-conversion; we can't recover the
  original % so it's a single-point curve under key "0").
- jaeger-jetflex-td-65-2-g-epdm-1000.json — extracted from the Jäger
  EPDM-1000mm SSOTE/DWP chart on the data sheet (vector-PDF read).
  SSOTE 8.20→6.40 %/m, DWP 25→48 mbar across Q 2-12 Nm³/h. Single
  coverage (vendor doesn't state test conditions).
- aerostrip-phoenix.json — 4-coverage SOTE family at 4.75 m water
  depth (DD 5/10/15/20 %, flux 10-70 Nm³/h·m²) from the Entec/de
  Winter 2023-11-22 dataset; DWP curve from the 21 % @ 4.05 m chart.
- pik300.json / prk300.json — 5-coverage SOTE + SSOTR (DD 5-25 %)
  with split DWP per model variant, water depth ≈ 4.0 m inferred from
  the SOTE↔SSOTR ratio in the source spreadsheet.

src/configs/diffuser.json:
- New asset.{model, assetTagNumber} block so the editor's selected
  model id survives validation.
- diffuser.density description corrected to "Bottom coverage [%]";
  default 2.4 → 15 (typical fine-bubble install).

src/configs/{rotatingMachine,valve}.json: small alignment edits that
came with the registry phase.

src/menu/asset.js + src/menu/aquonSamples.js: rewritten as facades
over assetResolver, keeping the editor-side cascade behaviour intact.

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

src/registry/backends/HttpBackend.js

@@ -0,0 +1,41 @@
+'use strict';
+
+/**
+ * HttpBackend — stub. The shape that any future remote product/asset DB will
+ * implement so the resolver can swap backends without touching consumers.
+ *
+ * Disabled by default. Set EVOLV_ASSET_REMOTE=1 to opt in; even then this
+ * stub throws on use because the upstream API is not yet defined. See
+ * `assetApiConfig.js` for the URL/auth scaffolding that will eventually
+ * land here.
+ */
+class HttpBackend {
+    constructor({ url, headers = {}, namespace } = {}) {
+        this.url = url;
+        this.headers = headers;
+        this.namespace = namespace;
+    }
+
+    static get enabled() {
+        return process.env.EVOLV_ASSET_REMOTE === '1';
+    }
+
+    loadAll() {
+        if (!HttpBackend.enabled) {
+            throw new Error(
+                'HttpBackend disabled (set EVOLV_ASSET_REMOTE=1 to enable); ' +
+                'no synchronous remote fetch is implemented yet.',
+            );
+        }
+        throw new Error(
+            'HttpBackend.loadAll(): remote asset backend not yet implemented. ' +
+            'Use FileBackend or implement this method against the WBD product API.',
+        );
+    }
+
+    async refresh() {
+        return this.loadAll();
+    }
+}
+
+module.exports = HttpBackend;