CSV Export

We're almost done! Our web crawler now extracts rich data from every page and stores it efficiently in a dictionary. But printing this data to the console isn't very useful for analysis. Let's export it to CSV format so its easier to read and parse.

For example, from this page data dictionary:

pages := map[string]PageData{
    "blog.boot.dev": {
        URL:            "https://blog.boot.dev",
        H1:             "Learn Backend Development",
        FirstParagraph: "Boot.dev teaches backend development...",
        OutgoingLinks:  []string{"https://boot.dev/courses", "https://boot.dev/about"},
        ImageURLs:      []string{"https://blog.boot.dev/logo.png"},
    },
}

We want to create a CSV file with columns: page_url, h1, first_paragraph, outgoing_link_urls, image_urls

Assignment

Create a new file called csv_report.go.
Import Go's built-in encoding/csv package:

import "encoding/csv"

Create a new function called write_csv_report. Here's the signature:

func writeCSVReport(pages map[string]PageData, filename string) error:

pages is the map returned by your crawler (keys are normalized URLs, values are PageData structs)
filename is the CSV file to create (defaults to "report.csv" in main.go)

Implement the writeCSVReport function. It should:
- Create a CSV with these column headers: page_url, h1, first_paragraph, outgoing_link_urls, image_urls
- Join slice values with semicolons (;) for the link and image URL columns

Here are some tips to get you started:

Open the file with os.Create(filename)
Use csv.NewWriter(file) to write the data
Write the header row with writer.Write([]string{...})
For each PageData in the map, write a row with its fields
Join slices with semicolons: strings.Join(page.OutgoingLinks, ";")

Update your main.go to use the CSV export:
- Import your writeCSVReport function
- After crawling completes, call writeCSVReport(cfg.pages, "report.csv")
- Remove any console printing of individual page details
Test your implementation:
- Verify report.csv is created after running the crawler
- Check that it opens properly in a spreadsheet program
- Ensure data is properly formatted with no broken rows

Run and submit the CLI tests.