Keep albums in the catalog: export folders and what went into them

An album is a named export destination. Its folder holds only the
exported files; the catalog records, per file, the image it was
rendered from, so an album can show the originals behind its JPEGs
(FR-EXP-10).

The tables are created on first use (CREATE TABLE IF NOT EXISTS), the
way dedup_probes is, rather than by a schema migration: a new
user_version makes every older build refuse this catalog's snapshot at
sync, and the 0.16.0 tablet would stop merging collections, keywords
and people for a feature it does not have.

Albums merge as collections do: by uuid and revision, tombstones on
delete, exports as a set union keyed on the server's file id (content
hash for a folder library). A folder on the server lives on the album
row and syncs; a folder on this device lives in album_folders, which
the merge never reads and the upload snapshot drops, because a path or
a SAF grant on one device means nothing on another.

Exports are keyed on the file name, not the image: two crops of one
photograph are two files and two rows, and an overwrite re-points the
name at whatever wrote it last.

core/dr-catalog/src/lib.rs

@@ -36,6 +36,7 @@ use std::path::Path;
 use dr_types::{Availability, ImageId};
 use rusqlite::Connection;
 
+pub mod albums;
 pub mod bursts;
 pub mod cache;
 pub mod collections;
@@ -57,6 +58,7 @@ pub mod sync;
 pub mod trash;
 pub mod walk;
 
+pub use albums::{Album, AlbumId, Place};
 pub use cache::{Budget, Cache, DEFAULT_BUDGET_BYTES};
 pub use collections::{Collection, CollectionKind, TreeRow};
 pub use dedup::{seen_by_content, seen_by_metadata, set_content_hash};