feat: add "Skip to main content" link for keyboard and screen reader users

[Athulyakrishna-k1312]

Summary

Adds a "Skip to main content" accessible link as the first element
in both templates, satisfying WCAG 2.4.1 (Level A) for keyboard
and screen reader users.

Changes Made

• templates/index.html — added skip link at top of body, added id="main-content" to hero section
• templates/project.html — added skip link at top of body, added id="main-content" to main element
• static/style.css — added .skip-link and .skip-link:focus styles

Type of Change

• Style / UI change

Testing Done

• Opened app via python app.py
• Pressed Tab on page load — skip link appeared at top
• Pressed Enter — focus jumped to main content past navbar
• Tested on desktop (1280px) and mobile (375px)
• All 27 tests pass

Screenshots

• before

- after

Related Issue

Closes #81

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