Add redirects for most common 404s on Fern site

[hey-august]

Data as of 2026 08 12

slug	404s
/docs/eleven-api/libraries	651
/docs/web-api/web-api-v-1-0-documentation/	198
/docs/developer-resources/docs/developer-resources/bounties	189
/docs/available-countries-withdraw	171
/docs/api/welcome	117
/docs/payout-overview	99
/docs/api/technical-documentation/sandbox/sandbox-app	66
/docs/user-profiles	60
/docs/api/technical-documentation/sdks/pay-kit/android-getting-started	48
/docs/overview/capabilities/text-to-speech/voice-settings	41
/docs/api-reference	36
/docs/web-api/ref	36
/docs/api/network-api/operations/create-a-payment	33
/docs/eleven-agents/api-reference/twilio/outbound-cal	31
/docs/eleven-creative/products/studio/audio-native	24
/docs	24
/docs/web-api/authentication/client-portal-gateway/installation-authentication	24
/docs/web-api/flex-web-service/flex-web-service/	21
/docs/	18
/docs/0x-swap-api/introduction	15