Document that package.json aliases may target only direct subfolders of src (#21)

Follow-up to #20, which was merged before this landed.

bot-agents has no `package.json` `imports` aliases (`src/` is flat and everything imports relatively), so no code changes. This records the new rule in the docs:

- `.agents/memory/imports-aliases-barrels.md`: aliases may target only a direct subfolder of `src/` (its `index.ts` or a `#x/*` pattern); nothing outside `src/`, not `src/` itself, not deeper folders; such code imports relatively.
- `.agents/memory/tests-layout-vitest.md`: `tests/` reach the public entry through a relative import, not a `#plugin` alias.
- `.agents/skills/migrate-deno-repo/SKILL.md` and `AGENTS.md`: same rule.

`vp check`, `vp test`, and `damem doctor` pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #21
Reviewed-by: bot <noreply@capsulizers.com>
Co-authored-by: Danny Kim <temeddix@gmail.com>
Co-committed-by: Danny Kim <temeddix@gmail.com>

src/prepare.ts

@@ -5,9 +5,7 @@ import { prepareRuntime } from "./runtime.ts";
 
 const env = (name: string): string => {
   const value = process.env[name];
-  if (value === undefined || value === "") {
-    throw new Error(`${name} is not set`);
-  }
+  if (value === undefined || value === "") throw new Error(`${name} is not set`);
   return value;
 };