refactor: restructure workspace file organization (#121) (#122)

## Path Changes
- audit.log: memory/audit.log → log/audit.log
- projects.json: memory/projects.json → projects/projects.json
- prompts: roles/<project>/<role>.md → projects/prompts/<project>/<role>.md

## Files Updated
- lib/audit.ts - new audit log path
- lib/projects.ts - new projects.json path
- lib/dispatch.ts - new prompt instructions path
- lib/tools/project-register.ts - prompt scaffolding path
- lib/setup/workspace.ts - workspace scaffolding paths
- lib/context-guard.ts - projects.json path
- lib/tools/setup.ts - tool description
- lib/templates.ts - AGENTS.md template path references

## Documentation Updated
- README.md
- docs/ARCHITECTURE.md
- docs/ONBOARDING.md
- docs/QA_WORKFLOW.md
- docs/ROADMAP.md
- docs/TESTING.md

Addresses issue #121

lib/audit.ts

@@ -10,7 +10,7 @@ export async function log(
   event: string,
   data: Record<string, unknown>,
 ): Promise<void> {
-  const filePath = join(workspaceDir, "memory", "audit.log");
+  const filePath = join(workspaceDir, "log", "audit.log");
   const entry = JSON.stringify({
     ts: new Date().toISOString(),
     event,