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/schema.rs

@@ -64,7 +64,8 @@ diesel::table! {
     entity_photo_links (id) {
         id -> Integer,
         entity_id -> Integer,
-        file_path -> Text,
+        library_id -> Integer,
+        rel_path -> Text,
         role -> Text,
     }
 }
@@ -73,14 +74,15 @@ diesel::table! {
     favorites (id) {
         id -> Integer,
         userid -> Integer,
-        path -> Text,
+        rel_path -> Text,
     }
 }
 
 diesel::table! {
     image_exif (id) {
         id -> Integer,
-        file_path -> Text,
+        library_id -> Integer,
+        rel_path -> Text,
         camera_make -> Nullable<Text>,
         camera_model -> Nullable<Text>,
         lens_model -> Nullable<Text>,
@@ -97,18 +99,17 @@ diesel::table! {
         date_taken -> Nullable<BigInt>,
         created_time -> BigInt,
         last_modified -> BigInt,
+        content_hash -> Nullable<Text>,
+        size_bytes -> Nullable<BigInt>,
     }
 }
 
 diesel::table! {
-    knowledge_embeddings (id) {
+    libraries (id) {
         id -> Integer,
-        keyword -> Text,
-        description -> Text,
-        category -> Nullable<Text>,
-        embedding -> Binary,
+        name -> Text,
+        root_path -> Text,
         created_at -> BigInt,
-        model_version -> Text,
     }
 }
 
@@ -129,23 +130,11 @@ diesel::table! {
     }
 }
 
-diesel::table! {
-    message_embeddings (id) {
-        id -> Integer,
-        contact -> Text,
-        body -> Text,
-        timestamp -> BigInt,
-        is_sent -> Bool,
-        embedding -> Binary,
-        created_at -> BigInt,
-        model_version -> Text,
-    }
-}
-
 diesel::table! {
     photo_insights (id) {
         id -> Integer,
-        file_path -> Text,
+        library_id -> Integer,
+        rel_path -> Text,
         title -> Text,
         summary -> Text,
         generated_at -> BigInt,
@@ -171,7 +160,7 @@ diesel::table! {
 diesel::table! {
     tagged_photo (id) {
         id -> Integer,
-        photo_name -> Text,
+        rel_path -> Text,
         tag_id -> Integer,
         created_time -> BigInt,
     }
@@ -196,7 +185,8 @@ diesel::table! {
 diesel::table! {
     video_preview_clips (id) {
         id -> Integer,
-        file_path -> Text,
+        library_id -> Integer,
+        rel_path -> Text,
         status -> Text,
         duration_seconds -> Nullable<Float>,
         file_size_bytes -> Nullable<Integer>,
@@ -208,7 +198,11 @@ diesel::table! {
 
 diesel::joinable!(entity_facts -> photo_insights (source_insight_id));
 diesel::joinable!(entity_photo_links -> entities (entity_id));
+diesel::joinable!(entity_photo_links -> libraries (library_id));
+diesel::joinable!(image_exif -> libraries (library_id));
+diesel::joinable!(photo_insights -> libraries (library_id));
 diesel::joinable!(tagged_photo -> tags (tag_id));
+diesel::joinable!(video_preview_clips -> libraries (library_id));
 
 diesel::allow_tables_to_appear_in_same_query!(
     calendar_events,
@@ -218,9 +212,8 @@ diesel::allow_tables_to_appear_in_same_query!(
     entity_photo_links,
     favorites,
     image_exif,
-    knowledge_embeddings,
+    libraries,
     location_history,
-    message_embeddings,
     photo_insights,
     search_history,
     tagged_photo,