[Stage 1, Christmas shop]: Clarify task description and evaluation process

[branxy]

Simplify description, clarify evaluation process, + minor syntax/grammar fixes

🤔 This is a ...

• 🌟 New task
• 🌐 New module
• ⚙️ Update to an existing task
• 🔧 Update to an existing module
• 🔗 Update or addition of external resources or links
• 🐛 Fix in a task or related content
• 🛠 Fix in a module or related content
• ✏️ Fixed a typo or grammatical error
• 🔗 Fixed a broken link
• ❓ Other (specify: merged related headings, made the cross-check section more descriptive)

Description

• Brief Overview:
  Problem:

1. The .md files for Christmas shop tasks have a confusing semantic structure, particularly in part 1 and part 2 in the Cross-check section, where four different headings related to task evaluation are scattered across the file.
2. The cross-check criteria is too ambigious for part1 and part2. Explanation: this is the first practical website-coding task on the course. Many people get confused during cross-check when they see criteria like "the layout matches the design" and go hypercritical deducting points under the pretence that "if it's not matching the design the Figma, then it's wrong". It also encourages more hostility, all because the phrasing "layout matches Figma" is too vague. I've had too many people deduct points for trivial things like more grammatically correct line-breaks in headings, or because "the snowflakes on the bg-image are bigger than in Figma", that I completely lost the desire to proceed and am quitting the course due to not having the time & energy to fight every unjustified points deduction.

• Implementation Approach:

1. .md files restructuring and minor fixes:
   • merged related headings (e.g., moved #task-evaluation content into #cross-check as it only referenced the cross-check instructions).
   • fixed a typo in christmas-shop-part3 (corrected "marge" to "merge").
   • fixed broken internal links leading to #cross-check sections.
   • fixed headings hierarchy and semantics.
   • corrected "naked" external links inserted as plain text.
2. Cross-check criteria:
   • clarified the goal of the cross-check process: to help others learn.
   • provided a clear statement about what is considered non-critical deviation from design.

Checklist

• ✅ I have performed a self-review of my own code.
• 📝 I have commented my code, particularly in hard-to-understand areas.
• 🔧 I have made corresponding changes to the documentation (if applicable).
• 🚫 My changes generate no new warnings or errors.