azure-prepare: Function file naming and README/test updates for new functions

## Problem

When creating a new Azure Function, the default experience has several UX issues:

### Issue 1: Generic file naming

**Current behavior:**
- User asks to create a function with route `/api/random`
- Agent creates `src/functions/httpTrigger.js`

**Expected behavior:**
- File should be named after the route/function: `src/functions/random.js` or `src/functions/httpRandom.js`
- Generic `httpTrigger` doesn't convey what the function does

### Issue 2: README not updated for new function

**Current behavior:**
- Template README only documents the original template functions
- No mention of the new function that was just created
- User doesn't know how to run/test their new function

**Expected behavior:**
- README should be updated to include:
- New function name and route
- Example curl command to test it
- Any specific configuration needed

### Issue 3: Test files not updated

**Current behavior:**
- Test files (if any) only test template's original functions, which can be unit tests or user test files like test.http or testdata.json used by curl
- No tests scaffolded for the new function

**Expected behavior:**
- revised test files that include new function api or routes asked for by the user

## Suggested Updates to azure-prepare skill

### 1. File naming convention

In `generate.md` or function generation logic:
```markdown
## Function File Naming

Name function files after their route/purpose:
- Route `/api/random` → `src/functions/random.js`
- Route `/api/users` → `src/functions/users.js`
- Route `/api/health` → `src/functions/health.js`

Do NOT use generic names like `httpTrigger.js` unless it's the only function.
```

### 2. README update requirement

Add to generation workflow:
```markdown
## Post-Generation Updates

After creating a new function, update README.md:
1. Add function to "Available Endpoints" table
2. Add curl example for testing
3. Document any required environment variables
```

### 3. Test scaffolding

```markdown
## Test Updates

When creating a new function:
1. If test file exists, add test case for new function
2. If no tests, add comment in README: "TODO: Add tests for {function_name}"
```

## Impact

- Better developer experience
- Self-documenting projects
- Easier onboarding for new team members
- Reduced confusion about what functions exist and how to test them