Phase 3: Migrate application layer modules (build, content, forum, relay, filestorage)

[jessefreeman]

Scope:
Convert mid-tier domain modules from CoffeeScript to TypeScript after core is stable.

Included Areas:

• server/build/*
• server/content/*
• server/forum/*
• server/relay/*
• server/filestorage/*

Approach:

• Module-by-module migration with focused PR per subsystem
• Introduce shared types in a central types/ directory as patterns emerge
• Add minimal unit tests or integration harness for each subsystem where missing

Acceptance Criteria:

• All listed directories free of .coffee files
• Shared type definitions reduce duplication (no copy/paste interfaces)
• Lint and TypeScript compile succeed

Risks:

• Hidden runtime assumptions (implicit any) → captured via strict mode errors
• Large PR size → mitigate by subsystem batching

[jessefreeman]

Parent epic: #6