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/dispatch.ts

@@ -53,8 +53,7 @@ export type DispatchResult = {
 
 /**
  * Build the task message sent to a worker session.
- * Reads role-specific instructions from workspace/roles/<project>/<role>.md
- * with fallback to workspace/roles/default/<role>.md.
+ * Reads role-specific instructions from workspace/projects/prompts/<project>/<role>.md.
  */
 export async function buildTaskMessage(opts: {
   workspaceDir: string;
@@ -196,10 +195,8 @@ export async function dispatchTask(
 async function loadRoleInstructions(
   workspaceDir: string, projectName: string, role: "dev" | "qa",
 ): Promise<string> {
-  const projectFile = path.join(workspaceDir, "roles", projectName, `${role}.md`);
-  const defaultFile = path.join(workspaceDir, "roles", "default", `${role}.md`);
-  try { return await fs.readFile(projectFile, "utf-8"); } catch { /* fallback */ }
-  try { return await fs.readFile(defaultFile, "utf-8"); } catch { /* none */ }
+  const projectFile = path.join(workspaceDir, "projects", "prompts", projectName, `${role}.md`);
+  try { return await fs.readFile(projectFile, "utf-8"); } catch { /* none */ }
   return "";
 }