Codra-wide cleanup: reduce comment density, extract hardcoded constants, shrink code across all packages

[devarshishimpi]

Context

Companion cleanup pass to the workspace restructure tracked in #66. As each package (schema, core, db, models, provider-github, api, ui) and app (apps/worker, apps/dashboard) lands, apply this same pass to it: cut comment density, kill hardcoded constants, shrink code, with zero behavior change.

Goals

1. Bring comment density in each package/app toward ~3%.
2. Extract hardcoded constants/magic values into a dedicated constants/config file per package.
3. Refactor/shrink code where possible, same outputs, no behavior change.

Scope

• packages/schema
• packages/core
• packages/db
• packages/models
• packages/provider-github
• packages/api
• packages/ui
• apps/worker
• apps/dashboard

Non-goals

• No behavior changes anywhere.
• No new features, no prompt/gate/scoring changes, no visual redesign.