data: add Browserbase Founder Pack credits

[nwinkelman2]

Summary

• add the missing Browserbase entity and its ElevenLabs Founder Pack credit redemption offer
• preserve the public page's exact information boundary: no invented credit amount, duration, or separate consideration
• describe the supported Browserbase product surface and membership-gated redemption path from the first-party page

Closes #1227

Evidence

• https://www.browserbase.com/11labs-founder-pack

Verification

• exact pinned Sourcey catalog verifier: valid (1 entity, 0 programs, 1 offer)
• live identity context issued for the unchanged candidate
• git diff --check
• DCO signed-off commit