add smart accounts and multisig course

[alizeeshan1234]

Summary

• Add new Smart Accounts & Multisig course with 8 lessons
• Covers smart account fundamentals, architecture patterns, Squads v4 deep-dive, multisig mechanics, and SPL Token multisig
• Updates course config files (courses.ts, courses.json, course-overviews.json, lesson-meta-descriptions.json)

Lessons

1. Introduction — Why keypair-controlled accounts fall short and how smart accounts solve it
2. Smart Account Fundamentals — PDAs as keyless vaults, authorization patterns, role-based access
3. Smart Account Architecture — Permission models, upgradeability trade-offs, CPI composability
4. Squads Smart Account Program — Deep dive into Squads v4: account types, 36 instructions, vault PDAs, SDK integration
5. Multisig Fundamentals — M-of-N threshold model, proposal lifecycle, participant roles
6. Multisig Operations & Mechanics — Transaction lifecycle, config changes, vault management, spending limits
7. SPL Token Multisig Approach — Built-in token multisig, limitations, and when to use it vs Squads
8. Conclusion — Ecosystem overview, key takeaways, and next steps

Closes #112

Test plan

• Verify course renders correctly on the dashboard
• Check all 8 lessons load and display properly
• Confirm course overview page shows correct metadata