Keep the homepage curated and /projects complete

[sarthakagrawal927]

Outcome

• keeps four products in focus on the homepage
• moves complete 58-project enumeration exclusively to /projects
• removes the repeated maintained/past catalogs and SaaS Maker self-strip
• applies the same curated boundary to /index.md
• adds a four-spotlight build invariant and regression coverage

Verification

• public catalog validation and Site Health parity: 58 identities
• lint, 32 tests, typecheck, shared packages, and all builds passed
• browser evidence at 390, 768, and 1440: no overflow, 4 focused product links, 1 directory gateway
• /projects: 58 directory rows
• design review: 0 P0 / 0 P1

Closes #49