feat: Activity History system — full audit coverage, UI, AI tools

Infrastructure (Phase 1):
- AuditLog schema: add source, entityName, summary fields + index
- createAuditEntry() helper: auto-diff, auto-summary, fire-and-forget
- auditLog query router: list, getByEntity, getTimeline, getActivitySummary

Audit Coverage (Phase 2 — 14 routers, 50+ mutations):
- vacation: create, approve, reject, cancel, batch ops (8 mutations)
- user: create, updateRole, setPermissions, resetPermissions (5 mutations)
- entitlement: set, bulkSet (3 mutations)
- client: create, update, delete, batchUpdateSortOrder
- org-unit: create, update, deactivate
- country: create, update, createCity, updateCity, deleteCity
- management-level: createGroup, updateGroup, createLevel, updateLevel, deleteLevel
- settings: updateSystemSettings (sensitive fields sanitized), testSmtp
- blueprint: create, update, updateRolePresets, delete, batchDelete, setGlobal
- rate-card: create, update, deactivate, addLine, updateLine, deleteLine, replaceLines
- calculation-rules: create, update, delete
- effort-rule: create, update, delete
- experience-multiplier: create, update, delete
- utilization-category: create, update

Admin UI (Phase 3):
- /admin/activity-log page with global searchable timeline
- Filters: entity type, action, user, date range, text search
- Expandable before/after diff view per entry
- Summary cards showing top entity types by change count
- EntityHistory reusable component for entity detail pages
- Sidebar nav link with clock icon

AI Assistant (Phase 4):
- query_change_history tool: "Who changed project X?"
- get_entity_timeline tool: "What happened to resource Y?"

Regression: 283 engine + 37 staffing tests pass. TypeScript clean.

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

packages/api/src/router/index.ts

@@ -1,6 +1,7 @@
 import { createTRPCRouter } from "../trpc.js";
 import { allocationRouter } from "./allocation.js";
 import { assistantRouter } from "./assistant.js";
+import { auditLogRouter } from "./audit-log.js";
 import { calculationRuleRouter } from "./calculation-rules.js";
 import { blueprintRouter } from "./blueprint.js";
 import { chargeabilityReportRouter } from "./chargeability-report.js";
@@ -36,6 +37,7 @@ import { webhookRouter } from "./webhook.js";
 
 export const appRouter = createTRPCRouter({
   assistant: assistantRouter,
+  auditLog: auditLogRouter,
   dashboard: dashboardRouter,
   dispo: dispoRouter,
   effortRule: effortRuleRouter,