Flatten repo structure: move crawler/ to root, remove vqa/ and immoweb/

The crawler subdirectory was the only active project. Moving it to the
repo root simplifies paths and removes the unnecessary nesting. The
vqa/ and immoweb/ directories were legacy/unused and have been removed.

Updated .drone.yml, .gitignore, .claude/ docs, and skills to reflect
the new flat structure.

frontend/src/constants/colorSchemes.ts

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+// Color schemes for map visualization
+// Different color schemes for different metrics to improve clarity
+
+import { Metric } from "@/components/Parameters";
+
+// For metrics where LOW is GOOD (price, price per sqm): Green → Yellow → Red
+export const LOW_IS_GOOD_COLOR_STOPS: [number, string][] = [
+  [0, 'rgba(34, 197, 94, 0.7)'],   // Green - good deal
+  [25, 'rgba(132, 204, 22, 0.7)'], // Lime
+  [50, 'rgba(250, 204, 21, 0.7)'], // Yellow - neutral
+  [75, 'rgba(249, 115, 22, 0.7)'], // Orange
+  [100, 'rgba(239, 68, 68, 0.7)'], // Red - expensive
+];
+
+// For metrics where HIGH is GOOD (size, rooms): Red → Yellow → Green
+export const HIGH_IS_GOOD_COLOR_STOPS: [number, string][] = [
+  [0, 'rgba(239, 68, 68, 0.7)'],   // Red - small
+  [25, 'rgba(249, 115, 22, 0.7)'], // Orange
+  [50, 'rgba(250, 204, 21, 0.7)'], // Yellow - medium
+  [75, 'rgba(132, 204, 22, 0.7)'], // Lime
+  [100, 'rgba(34, 197, 94, 0.7)'], // Green - large
+];
+
+// Legacy color stops (for backwards compatibility)
+export const LEGACY_COLOR_STOPS: [number, string][] = [
+  [0, 'rgba(0,185,243,0)'],
+  [25, 'rgba(0,185,243,0.24)'],
+  [60, 'rgba(255,223,0,0.3)'],
+  [100, 'rgba(255,105,0,0.3)'],
+];
+
+// Get the appropriate color scheme based on metric type
+export function getColorSchemeForMetric(metric: Metric | string): [number, string][] {
+  switch (metric) {
+    case Metric.qmprice:
+    case Metric.price:
+    case 'qmprice':
+    case 'total_price':
+      // Lower price is better → Green for low, Red for high
+      return LOW_IS_GOOD_COLOR_STOPS;
+
+    case Metric.qm:
+    case Metric.rooms:
+    case 'qm':
+    case 'rooms':
+      // Higher value is better → Green for high, Red for low
+      return HIGH_IS_GOOD_COLOR_STOPS;
+
+    default:
+      return LOW_IS_GOOD_COLOR_STOPS;
+  }
+}
+
+// Get interpretation text for legend
+export function getMetricInterpretation(metric: Metric | string): { low: string; high: string; name: string } {
+  switch (metric) {
+    case Metric.qmprice:
+    case 'qmprice':
+      return { low: 'Good deal', high: 'Expensive', name: 'Price per m²' };
+
+    case Metric.price:
+    case 'total_price':
+      return { low: 'Good deal', high: 'Expensive', name: 'Total Price' };
+
+    case Metric.qm:
+    case 'qm':
+      return { low: 'Small', high: 'Large', name: 'Size (m²)' };
+
+    case Metric.rooms:
+    case 'rooms':
+      return { low: 'Few rooms', high: 'Many rooms', name: 'Bedrooms' };
+
+    default:
+      return { low: 'Low', high: 'High', name: 'Value' };
+  }
+}
+
+// Color scheme names for display
+export const COLOR_SCHEME_NAMES = {
+  LOW_IS_GOOD: 'Green → Red (low is good)',
+  HIGH_IS_GOOD: 'Red → Green (high is good)',
+  LEGACY: 'Classic (blue → orange)',
+} as const;

frontend/src/constants/index.ts

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+// Application constants and configuration
+
+// Re-export color schemes
+export * from './colorSchemes';
+
+// API endpoints
+export const API_ENDPOINTS = {
+  LISTING_GEOJSON: '/api/listing_geojson',
+  LISTING_GEOJSON_STREAM: '/api/listing_geojson/stream',
+  REFRESH_LISTINGS: '/api/refresh_listings',
+  TASK_STATUS: '/api/task_status',
+  TASKS_FOR_USER: '/api/tasks_for_user',
+  CANCEL_TASK: '/api/cancel_task',
+  CLEAR_ALL_TASKS: '/api/clear_all_tasks',
+  GET_DISTRICTS: '/api/get_districts',
+} as const;
+
+// Map configuration
+export const MAP_CONFIG = {
+  MAPBOX_TOKEN: import.meta.env.VITE_MAPBOX_TOKEN || 'pk.eyJ1IjoiZGktdG8iLCJhIjoiY2o0bnBoYXcxMW1mNzJ3bDhmc2xiNWttaiJ9.ZccatVk_4shzoAsEUXXecA',
+  DEFAULT_CENTER: [13.38032, 49.994210] as [number, number],
+  DEFAULT_ZOOM: 5,
+  STYLE: 'mapbox://styles/mapbox/light-v9',
+} as const;
+
+// Heatmap configuration
+export const HEATMAP_CONFIG = {
+  INTENSITY: 9,
+  SPREAD: 0.05,
+  CELL_DENSITY: 0.5, // Smaller value = bigger hexagons
+} as const;
+
+// Percentile configuration for data visualization
+export const PERCENTILE_CONFIG = {
+  MIN_BOUND: 0.05, // 5th percentile for color scale minimum
+  MAX_BOUND: 0.95, // 95th percentile for color scale maximum
+  BOUNDS_CLIP_MIN: 0.01, // 1st percentile for bounding box
+  BOUNDS_CLIP_MAX: 0.99, // 99th percentile for bounding box
+} as const;
+
+// Heatmap color gradient stops
+export const HEATMAP_COLOR_STOPS: [number, string][] = [
+  [0, 'rgba(0,185,243,0)'],
+  [25, 'rgba(0,185,243,0.24)'],
+  [60, 'rgba(255,223,0,0.3)'],
+  [100, 'rgba(255,105,0,0.3)'],
+];
+
+// Default form values
+export const DEFAULT_FORM_VALUES = {
+  min_bedrooms: 1,
+  max_bedrooms: 3,
+  max_price: 3000,
+  min_price: 2000,
+  min_sqm: 50,
+  last_seen_days: 28,
+} as const;
+
+// Polling intervals
+export const POLLING_INTERVALS = {
+  TASK_STATUS_MS: 5000, // 5 seconds
+} as const;