feat: multi-library foundation (schema + libraries module)

Adds a `libraries` registry table and threads library_id through
per-instance metadata tables (image_exif, photo_insights,
entity_photo_links, video_preview_clips). File-path columns renamed to
rel_path to make the relative-to-root semantics explicit. Adds
content_hash + size_bytes on image_exif to support future hash-keyed
thumbnail/HLS dedup. Tags and favorites stay library-agnostic so they
share across libraries by rel_path.

Behavior is unchanged: a single primary library (id=1) is seeded from
BASE_PATH on first boot; all handlers and DAOs route through it as a
transitional shim until the API gains a library query param.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/database/models.rs

@@ -1,6 +1,6 @@
 use crate::database::schema::{
-    entities, entity_facts, entity_photo_links, favorites, image_exif, photo_insights, users,
-    video_preview_clips,
+    entities, entity_facts, entity_photo_links, favorites, image_exif, libraries, photo_insights,
+    users, video_preview_clips,
 };
 use serde::Serialize;
 
@@ -23,6 +23,7 @@ pub struct User {
 #[diesel(table_name = favorites)]
 pub struct InsertFavorite<'a> {
     pub userid: &'a i32,
+    #[diesel(column_name = rel_path)]
     pub path: &'a str,
 }
 
@@ -30,12 +31,15 @@ pub struct InsertFavorite<'a> {
 pub struct Favorite {
     pub id: i32,
     pub userid: i32,
+    #[diesel(column_name = rel_path)]
     pub path: String,
 }
 
 #[derive(Insertable)]
 #[diesel(table_name = image_exif)]
 pub struct InsertImageExif {
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub camera_make: Option<String>,
     pub camera_model: Option<String>,
@@ -53,11 +57,16 @@ pub struct InsertImageExif {
     pub date_taken: Option<i64>,
     pub created_time: i64,
     pub last_modified: i64,
+    pub content_hash: Option<String>,
+    pub size_bytes: Option<i64>,
 }
 
+// Field order matches the post-migration column order in `image_exif`.
 #[derive(Serialize, Queryable, Clone, Debug)]
 pub struct ImageExif {
     pub id: i32,
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub camera_make: Option<String>,
     pub camera_model: Option<String>,
@@ -75,11 +84,15 @@ pub struct ImageExif {
     pub date_taken: Option<i64>,
     pub created_time: i64,
     pub last_modified: i64,
+    pub content_hash: Option<String>,
+    pub size_bytes: Option<i64>,
 }
 
 #[derive(Insertable)]
 #[diesel(table_name = photo_insights)]
 pub struct InsertPhotoInsight {
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub title: String,
     pub summary: String,
@@ -92,6 +105,8 @@ pub struct InsertPhotoInsight {
 #[derive(Serialize, Queryable, Clone, Debug)]
 pub struct PhotoInsight {
     pub id: i32,
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub title: String,
     pub summary: String,
@@ -102,6 +117,24 @@ pub struct PhotoInsight {
     pub approved: Option<bool>,
 }
 
+// --- Libraries ---
+
+#[derive(Serialize, Queryable, Clone, Debug)]
+pub struct LibraryRow {
+    pub id: i32,
+    pub name: String,
+    pub root_path: String,
+    pub created_at: i64,
+}
+
+#[derive(Insertable)]
+#[diesel(table_name = libraries)]
+pub struct InsertLibrary<'a> {
+    pub name: &'a str,
+    pub root_path: &'a str,
+    pub created_at: i64,
+}
+
 // --- Knowledge memory models ---
 
 #[derive(Insertable)]
@@ -162,6 +195,8 @@ pub struct EntityFact {
 #[diesel(table_name = entity_photo_links)]
 pub struct InsertEntityPhotoLink {
     pub entity_id: i32,
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub role: String,
 }
@@ -170,6 +205,8 @@ pub struct InsertEntityPhotoLink {
 pub struct EntityPhotoLink {
     pub id: i32,
     pub entity_id: i32,
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub role: String,
 }
@@ -177,6 +214,8 @@ pub struct EntityPhotoLink {
 #[derive(Insertable)]
 #[diesel(table_name = video_preview_clips)]
 pub struct InsertVideoPreviewClip {
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub status: String,
     pub created_at: String,
@@ -186,6 +225,8 @@ pub struct InsertVideoPreviewClip {
 #[derive(Serialize, Queryable, Clone, Debug)]
 pub struct VideoPreviewClip {
     pub id: i32,
+    pub library_id: i32,
+    #[diesel(column_name = rel_path)]
     pub file_path: String,
     pub status: String,
     pub duration_seconds: Option<f32>,