Break out source files from generated files

[danielporterda]

Problem: Source and generated files are confusing in the same folder. Moving sources broke the editor (#1585, backed out in #1598).

Solution: Put sources in a separate folder within Mintlify's content tree and register them as hidden pages so they remain editable.

1. Keep ordinary pages, navigation, and images directly editable.
2. Move network source pages into docs-main/sources/, mark them hidden, and map each to its public output.
3. Regenerate, validate, and preview public outputs after editor saves.
4. Preserve concurrent saves and flag direct edits to generated outputs.
5. Pilot one page through editing, saving, and generation before expanding. Hidden-page visibility is confirmed; the new folder and round-trip preservation still need testing.

Downside: For generated pages, editor users must edit the hidden source file. They may mistakenly edit the visible generated page instead, so validation must catch those edits and direct them to the source.