Initial commit: pi-project-map skill scaffolding

- Design doc with full spec (dense markdown format, hybrid AST+LLM pipeline,
  consumption model, stale data mitigation)
- Implementation plan with 6 milestones and rollout strategy
- TypeScript package structure with all source stubs
- CLI entry point, formatter, discover, init, patch, validate, extract, merge
- Pi SKILL.md with tool definitions and format documentation

hooks/on-prompt.ts

@@ -0,0 +1,11 @@
+// Pi skill prompt hook
+// Injected into every prompt to remind the agent to maintain .pi-map.md files
+
+export const MAINTENANCE_INSTRUCTION = `
+If you modify any source file, run \`project-map:patch <file-path>\` to update the analysis.
+If you suspect staleness, run \`project-map:validate\`.
+`;
+
+export function injectPrompt(originalPrompt: string): string {
+  return `${originalPrompt}\n\n---\n${MAINTENANCE_INSTRUCTION}`;
+}