refactor: compile the crate once — main.rs uses the library

main.rs re-declared nearly every module (`mod ai; mod database; …`)
that lib.rs also declared, so the ~100k-line crate compiled twice in
every build (lib for the src/bin tools, bin for the server) and the
test suite ran most tests twice. watcher.rs even reached into the lib
copy via `image_api::` from inside the bin copy.

The six bin-only modules (backfill, handlers, hls_stats, knowledge,
reels, watcher) move into lib.rs; main.rs keeps only startup wiring
over `use image_api::…`. A few items main calls become `pub`, and the
dead_code allowances that only existed because each copy saw half the
callers are gone. CLAUDE.md says not to reintroduce `mod` in main.rs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/database/reconcile.rs

@@ -26,11 +26,6 @@
 //! The pass operates on the database alone — no filesystem access —
 //! so it doesn't need the library availability gate.
 
-// The lib doesn't call into this module directly — the watcher (in the
-// bin) does. Dead-code analysis at the lib level can't see that, so
-// suppress at the module level. Tests still exercise every function.
-#![allow(dead_code)]
-
 use diesel::prelude::*;
 use diesel::sql_query;
 use diesel::sqlite::SqliteConnection;