# Allow empty content in POST /api/docs

## Description

## Summary

POST /api/docs (document creation) currently rejects empty content strings.

## Current Behavior

```typescript
// src/serve/routes/api.ts:682
if (\!body.content || typeof body.content \!== 'string') {
  return errorResponse('VALIDATION', 'Missing or invalid content');
}
```

The `\!body.content` check rejects empty string `''` because it's falsy.

## Proposed Change

```typescript
if (typeof body.content \!== 'string') {
  return errorResponse('VALIDATION', 'Missing or invalid content');
}
```

This matches PUT /api/docs/:id (update) which already allows empty content:

```typescript
// src/serve/routes/api.ts:545-546
if (typeof body.content \!== 'string') {
  return errorResponse('VALIDATION', 'Missing or invalid content');
}
```

## Use Case

Users may want to create placeholder files or empty notes for later filling in.

## Files to Change

- src/serve/routes/api.ts - fix validation
- Add test case for empty content creation

## Acceptance

- [ ] Implementation complete
- [ ] Tests passing
- [ ] Documentation updated

## Done summary

TBD

## Evidence

- Commits:
- Tests:
- PRs:
