Add shared types package

Shared TypeScript types, Zod validators, API contract definitions,
and constants used by both server and UI. Covers agents, goals,
issues, projects, and activity entities.

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

packages/shared/src/validators/index.ts

@@ -0,0 +1,27 @@
+export {
+  createAgentSchema,
+  updateAgentSchema,
+  type CreateAgent,
+  type UpdateAgent,
+} from "./agent.js";
+
+export {
+  createProjectSchema,
+  updateProjectSchema,
+  type CreateProject,
+  type UpdateProject,
+} from "./project.js";
+
+export {
+  createIssueSchema,
+  updateIssueSchema,
+  type CreateIssue,
+  type UpdateIssue,
+} from "./issue.js";
+
+export {
+  createGoalSchema,
+  updateGoalSchema,
+  type CreateGoal,
+  type UpdateGoal,
+} from "./goal.js";