Fix typos and SQL query issues in codebase

[Copilot]

This PR addresses several small but important issues found during codebase review:

Changes

1. Fixed comment typo in server/Models/Broadcast.cs

Corrected a grammatical error in the comment explaining the broadcast creation process:

• Changed "The the email" to "Then the email" on line 8

2. Fixed SQL query schema prefix in server/Models/Broadcast.cs

Added missing schema prefix in the ContactCount method's SQL query:

• Changed tags.slug to mail.tags.slug on line 62
• This ensures consistency with other table references in the query (mail.contacts, mail.tagged, mail.tags)

3. Fixed template string formatting in cli/bin/mdmail-broadcast.js

Corrected a malformed template string in the default email body:

• Added missing opening quote before "SendAt" on line 71
• The string now correctly reads: "SendAt" in the frontmatter

Testing

• ✅ The .NET project builds successfully with no new errors or warnings
• ✅ All changes are backward compatible
• ✅ No functional changes to application behavior

These minimal fixes improve code quality and prevent potential issues with SQL queries when filtering broadcasts by tags.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Issues with issuess</issue_title>
<issue_description>- Understnd the codebase

• Make some changes
• </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #55

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.