data: add AnnounceKit startup program

[infser]

Summary

• Adds entities/an/announcekit.yaml for AnnounceKit Startup Program.
• Closes Missing record: AnnounceKit Startup Program #893.
• First-party https://announcekit.app/startup: 50% off any AnnounceKit plan for 12 months (Essentials/Growth/Scale), early-stage eligibility (<5 employees, <2 years, ≤$1M funding), all features included.

Verification

• No existing announcekit entity on main.
• No open AnnounceKit PR (prior data: add AnnounceKit startup discount offer #900/catalog: add AnnounceKit startup program #42 closed).
• Amounts taken only from the live first-party startup page.
• Summaries ≤240 chars; no email addresses in instructions; DCO Signed-off-by.