refactor(t-paliad-184): EventDeadlineService.Calculate delegates

Phase 3 Slice 3 service-side rewire. EventDeadlineService.Calculate
now:

  1. Looks up trigger event metadata (unchanged — the legacy response
     shape still carries TriggerEvent + TriggerDate at the top level).
  2. SELECTs source event_deadlines rows for the trigger to recover
     (id, duration, alt_*, combine_op, notes_en) — the unified
     UIResponse drops those fields. SELECT is still allowed by the
     mig 086 read-only trigger; only writes are blocked.
  3. Delegates the rule SELECT + math to FristenrechnerService.Calculate
     with TriggerEventIDFilter set.
  4. Merges the unified result with the source rows (join by Name =
     title_de) to produce the legacy EventDeadlineResult shape with
     ID, ruleCodes, isComposite, compositeNote intact.
  5. Loads rule_codes from event_deadline_rule_codes (also still
     readable) by source.id.

Public signature unchanged — /api/tools/event-deadlines callers see
no diff. The legacy applyDuration / addWorkingDays helpers stay on
EventDeadlineService for the pure-Go unit tests + the composite-note
leg-pick that the unified UIDeadline doesn't expose.

main.go wiring: NewEventDeadlineService gains the FristenrechnerService
dependency.

cmd/server/main.go

@@ -147,7 +147,13 @@ func main() {
 			Calculator:     services.NewDeadlineCalculator(holidays),
 			Users:          users,
 			Fristenrechner: services.NewFristenrechnerService(rules, holidays, courts),
-			EventDeadline:  services.NewEventDeadlineService(pool, services.NewDeadlineCalculator(holidays), holidays, courts),
+			EventDeadline: services.NewEventDeadlineService(
+				pool,
+				services.NewDeadlineCalculator(holidays),
+				holidays,
+				courts,
+				services.NewFristenrechnerService(rules, holidays, courts),
+			),
 			Courts:         courts,
 			DeadlineSearch: services.NewDeadlineSearchService(pool),
 			EventCategory:  nil, // wired below; cross-link order matters