feat(setup/project-init): initialize TypeScript ESM project skeleton

- package.json with @alkdev/taskgraph, ESM primary, CJS compat exports
- tsconfig.json targeting Node 18+, strict mode, declaration output
- All production deps: graphology suite, @alkdev/typebox, yaml
- Dev deps: typescript, vitest, @types/node
- src/ skeleton: schema, graph, analysis, frontmatter, error modules
- test/ directory with 5 placeholder test files
- .gitignore and vitest.config.ts

src/graph/construction.ts

@@ -0,0 +1,5 @@
+// TaskGraph class construction — fromTasks, fromRecords, fromJSON, incremental building
+
+export class TaskGraph {
+  // Stub — implementation pending
+}