feat: initial Münster Haushalt icicle viewer

Editorial single-page viewer for the City of Münster's 2026/2027
budget draft, built as an Astro v6 SPA with a 4-level zoomable
icicle (Produktbereich → Produktgruppe → Category → Breakdown).

Highlights:
- Multi-flow data layer over the official open-data CSVs
  (Aufwendungen + Erträge, 2008–2028) with overlap reconciliation
  across plan years.
- Year slider as a 21-year mini-histogram of both flows;
  drag-to-scrub and click-to-jump, with bars morphing via CSS
  transitions on SVG geometry attributes.
- Vertically centred icicle with year-outline rectangles framing
  each year's relative budget size, à la Bostock's animated treemap.
- Headline "ausgibt / einnimmt" toggle; sidebar Aufwendungen/Erträge
  rows double as flow toggles. Active flow in Aufwendungen-purple /
  Erträge-orange (OKLCH).
- Click-to-zoom via path-keyed lookup with ZOOM_COL_BOUNDS that
  reallocate the depth axis per zoom state. Zoomed item moves to the
  sidebar; canvas shows its descendants only (no adjacent-block leaks).
- Sidebar shows path-specific Aufwendungen/Erträge/Saldo plus the
  source-PDF Beschreibung; Erläuterungen behind a collapsed details.
- Build-time PDF extraction (scripts/extract-pg-sections.mjs) parses
  68 Produktgruppen' Beschreibung + Erläuterungen sections from
  Band 1, including 10 cells of structured Mio.-€ breakdowns
  (Steuern, Transferaufwendungen, etc.) that drive the level-4 view.
- URL state sync for path, year, and flow via history.replaceState
  so any zoom is shareable.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -0,0 +1,29 @@
+{
+  "name": "ms-haushalt",
+  "type": "module",
+  "version": "0.0.1",
+  "engines": {
+    "node": ">=22.12.0"
+  },
+  "scripts": {
+    "dev": "astro dev",
+    "build": "astro build",
+    "preview": "astro preview",
+    "astro": "astro"
+  },
+  "dependencies": {
+    "@fontsource-variable/geist": "^5.2.8",
+    "@fontsource-variable/geist-mono": "^5.2.7",
+    "astro": "^6.2.2",
+    "d3-dsv": "^3.0.1",
+    "d3-hierarchy": "^3.1.2"
+  },
+  "devDependencies": {
+    "@astrojs/check": "^0.9.9",
+    "@types/d3-dsv": "^3.0.7",
+    "@types/d3-hierarchy": "^3.1.7",
+    "@types/node": "^25.6.0",
+    "tsx": "^4.21.0",
+    "typescript": "^6.0.3"
+  }
+}