Add footer

[AJaccP]

🧠 Context

No footer exists yet. The app layout lives in src/App.tsx — it's a full-height flex column with a <Header /> at the top and a <main> that fills the remaining space. The footer should sit below <main>

The footer should contain:

• The full CCSS logo (SVG asset — ask Jacc for the asset)
• Copyright line using the current year dynamically: © {new Date().getFullYear()} Carleton Computer Science Society
• A link to the GitHub repository: https://github.com/CarletonComputerScienceSociety/course-graph
• Two short disclaimer lines:
  • "Not affiliated with or endorsed by Carleton University."
  • "Always verify course requirements in the official undergraduate calendar."

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🛠️ Implementation Plan

1. Place the logo asset at src/assets/ccss-logo.svg (ask Jacc for the file).

2. Model the visual design after the footer on ccss.carleton.ca — our footer will have less content but should follow the same general layout and style.

3. Create src/components/Footer.tsx and wire it into src/App.tsx below <main>.

4. Run pnpm dev and check that the footer appears on both /explorer and /planner. Verify <main> still fills the remaining height correctly and the footer doesn't overlap content.

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✅ Acceptance Criteria

• Footer is visible on both the Explorer and Planner routes
• Contains CCSS logo
• Copyright year is dynamic (new Date().getFullYear()) — not hardcoded
• Contains a working link to the GitHub repository
• Contains the disclaimer "Not affiliated with or endorsed by Carleton University."
• Contains "Always verify course requirements in the official undergraduate calendar."
• Main content area still fills available height correctly — footer does not overlap the graph or planner grid