feat: add Entrepreneurship & Startup notes for Sem 7

[Apurva-Lakhe]

Related Issue

Fixes #180

##Description
Added complete study materials for Entrepreneurship & Startup (Semester 7) which was previously marked as "Coming Soon" on the website.
Changes made:

• Created app/sem7/eas/ folder with full Next.js route structure
• Added constants.ts with all chapter and subtopic definitions
• Added layout.tsx wrapping the sidebar and main content
• Added components/Sidebar.tsx with collapsible mobile-friendly navigation
• Added [chapter]/page.tsx dynamic route handling all chapters and subtopics
• Added content files for all 4 units:
  ~chapter0.tsx — Course Outline with syllabus overview and reference books
  ~chapter1.tsx — Fundamentals of Entrepreneurship (concept, characteristics, types, functions, women entrepreneurship)
  ~chapter2.tsx — Startup Ecosystem (concept of startup, types, ecosystem)
  ~chapter3.tsx — Ideation and Design Thinking (SCAMPER, Brainstorming, Prototyping)
  ~chapter4.tsx — Funding and Sustainability (angel funding, venture capital, ownership, failure causes)
  -Updated app/components/subjects.tsx to activate the subject link and fix a code conflict ("es" was used for both Environmental Studies and Entrepreneurship & Startup, changed to "eas")

##Type of Change

• Bug fix
• New feature
• Documentation update
• UI/UX improvement
• Refactor

##Screenshots / Demo:

##How Has This Been Tested?

• Ran npm run dev locally and visited all chapter routes:
  /sem7/eas/ch0 — Course Outline
  /sem7/eas/ch1 — Unit 1
  /sem7/eas/ch2 — Unit 2
  /sem7/eas/ch3 — Unit 3
  /sem7/eas/ch4 — Unit 4
• Verified sidebar navigation works on both desktop and mobile
• Verified Previous/Next navigation works across all chapters
• Verified the subject card on the homepage links correctly to /sem7/eas/ch0

##Checklist

• My code follows the project structure and conventions
• I have tested the changes locally
• I have linked the related issue properly
• I have added screenshots where applicable
• No existing functionality was broken

##AI Usage

• I have used AI tools (ChatGPT, Copilot, Claude, etc.) and I have reviewed, verified, and understood all generated code/content before submitting this PR
  If AI tools were used, briefly explain how:
  Used Claude (Anthropic) to scaffold the folder structure of content files matching the existing project conventions. All code and content was reviewed, verified against the existing codebase structure, and understood before submission. Subject content was cross-verified with the provided syllabus and reference books (Entrepreneurial Development by S.S. Khanka and Anil Kumar).

##Additional Notes

• The subject code was changed from "es" to "eas" in subjects.tsx to avoid conflict with Environmental Studies which also used "es"

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