feat: unified error handling + AI service modularisation

Error handling (Prompt 2):
- src/services/errors.ts: AppError class, normalizeError(), throwServiceError() helper
- 6 services wrapped with try/catch (property, match, need, shortlist, futureSignal, inquiry)
- inquiryService aligned from custom ServiceResult<T> to standard ServiceResponse types
- Results, MatchCenter, FutureAvailability pages show <ErrorState onRetry> on query failure

AI modularisation (Prompt 3):
- src/services/aiService.ts reduced from 755 → 19 lines (barrel re-export)
- src/services/ai/IAIService.ts: typed interface + all response types
- src/services/ai/mock/: needParser, compareBuilder, decisionBrief, listingParser, MockAIService
- src/services/ai/openrouter/OpenRouterAIService.ts: model-agnostic skeleton
- src/services/ai/prompts/: 4 prompt template files (needParsing, matchExplanation, compareSummary, decisionBrief)
- src/services/ai/index.ts: factory selects Mock or OpenRouter via VITE_USE_REAL_AI flag
- All existing import paths unchanged — zero call-site modifications

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/supply/MatchCenter.tsx

@@ -15,6 +15,7 @@ import { useNeeds } from '../../hooks/useNeeds'
 import { useMatchCenterStore } from '../../stores/matchCenterStore'
 import { useToastStore } from '../../stores/toastStore'
 import { MatchListCard, MatchBriefingPanel, MatchCenterSkeleton } from '../../components/match-center'
+import { ErrorState } from '../../components/ui'
 import type { Match } from '../../domain/match'
 
 const STRENGTH_OPTIONS = [
@@ -32,7 +33,7 @@ const STATUS_OPTIONS = [
 ]
 
 export default function MatchCenter() {
-  const { data: matches = [], isLoading } = useMatches()
+  const { data: matches = [], isLoading, isError, refetch } = useMatches()
   const { data: properties = [] } = useProperties()
   const { data: needs = [] } = useNeeds()
   const { setSelectedProperty, setSelectedNeed } = useMatchCenterStore()
@@ -141,6 +142,8 @@ export default function MatchCenter() {
       <Box sx={{ flex: 1, overflowY: 'auto', bgcolor: '#f8fafc' }}>
         {isLoading ? (
           <MatchCenterSkeleton />
+        ) : isError ? (
+          <ErrorState onRetry={refetch} />
         ) : filtered.length === 0 ? (
           <Box sx={{ p: 6, textAlign: 'center' }}>
             <Typography color="text.secondary">Keine Matches für diese Filter.</Typography>