Followup to #183 to address bugs found after pulling into org

• The apiIndex file should be placed into the outpurDir specified by the consumer rather than in the astro dir to support monorepos properly
• If no tab name can be determined (such as for local files in the consuming repo) we need to supply a fallback, as currently this situation causes the build to crash during the prerendering step. Also we should probably add some problem handling around this in case other tabless edge cases are found.