Spring Cleaning

Full codebase health pass. Two phases, in order.

Phase 1: Subtract

"Should this still exist?"

Delete things. The codebase gets smaller.

1. Dead code — Unused functions, types, modules, imports, variables, and constants. If nothing calls it, remove it.
2. Unused dependencies — Dependencies in the manifest that aren't imported anywhere. Remove them.
3. Backwards compatibility shims — Deprecated APIs, migration helpers, legacy type aliases, re-exports kept only for old consumers. If the migration window has passed, remove them.
4. Abandoned experiments — Half-finished features behind dead flags, commented-out code blocks, modules that were started but never wired in.
5. Stale config — Environment variables, feature flags, or config keys that nothing reads anymore.
6. Orphaned files — Files that aren't imported, included, referenced, or served anywhere. Stale test fixtures, unused assets, leftover scripts, generated files that aren't regenerated.
7. Gitignore hygiene — Check .gitignore for patterns that no longer apply (removed tooling, old build dirs). Add missing patterns for things that shouldn't be tracked (build artifacts, editor files, OS files, secrets, .env).

Catalog (don't delete) TODOs and placeholders — search for TODO, FIXME, HACK, XXX, placeholder implementations. Present a list with location (file:line), brief description, and suggested priority.