onboarding: bar chart of files by language prior to upload

[greynewell]

What problem does this solve?

kdspodfkaodsf

Proposed solution

dfasdfadsf

Alternatives considered

No response

[greynewell]

Implemented in #64 — LanguageStats() + PrintLanguageBarChart() added to internal/files/zip.go. Printed to stderr before every API upload (both supermodel watch and supermodel analyze paths).