refactor: deduplicate modals, notifications, confirms, comboboxes, proficiency

Modal Overlay (Finding 1 — 6 admin files):
- Migrated CountriesClient, ManagementLevelsClient, OrgUnitsClient,
  CalculationRulesClient, UtilizationCategoriesClient, RoleModal
  from inline fixed-overlay to AnimatedModal component
- Gains: animated transitions, backdrop blur, escape key for free

Notification Helper (Finding 9 — 9 API files, 14 call sites):
- New createNotification() + createNotificationsForUsers() in
  packages/api/src/lib/create-notification.ts
- Handles exactOptionalPropertyTypes spread + SSE emit internally
- Simplified: budget-alerts, estimate-reminders, auto-staffing,
  vacation-conflicts, chargeability-alerts, comment, vacation, notification

ConfirmDialog (Finding 3 — 11 files):
- Replaced all window.confirm() calls with ConfirmDialog component
- Files: CommentThread, EffortRules, ExperienceMultipliers,
  ManagementLevels, CalculationRules, Countries, RateCards,
  ApplyEffortRules, ApplyExperienceMultipliers, NotificationCenter,
  ReminderModal

EntityCombobox (Finding 4 — 3 files):
- New generic EntityCombobox<T> with customization hooks
- ResourceCombobox + ProjectCombobox rewritten as thin wrappers
- All consumers unchanged (backwards-compatible props)

Proficiency Constants (Finding 2 — 2 files):
- SkillsAnalytics + SkillMarketplace now import from skills/shared.tsx
- Deleted ~70 LOC of local duplicate definitions

Regression: 283 engine + 37 staffing tests pass. TypeScript clean.
AI Assistant: all 87 tools verified accessible.

Co-Authored-By: claude-flow <ruv@ruv.net>

packages/api/src/index.ts

@@ -3,6 +3,7 @@ export { createTRPCContext, createTRPCRouter, createCallerFactory, publicProcedu
 export { eventBus, emitAllocationCreated, emitAllocationUpdated, emitAllocationDeleted, emitProjectShifted, emitBudgetWarning, flushPendingEvents, cancelPendingEvents } from "./sse/event-bus.js";
 export { logger } from "./lib/logger.js";
 export { anonymizeResource, anonymizeResources, anonymizeUser, getAnonymizationConfig, getAnonymizationDirectory } from "./lib/anonymization.js";
+export { createNotification, createNotificationsForUsers } from "./lib/create-notification.js";
 export { checkBudgetThresholds } from "./lib/budget-alerts.js";
 export { checkPendingEstimateReminders } from "./lib/estimate-reminders.js";
 export { checkChargeabilityAlerts } from "./lib/chargeability-alerts.js";