perf: migrate all user/session/auth IDs from VARCHAR(36) to native UUID

- Schema: all ~15 VARCHAR(36) columns → UUID with DEFAULT gen_random_uuid()
- Domain entities: User, Session, DeviceCode, AppPassword, Share → id: Uuid
- DTOs: CurrentUser.id → Uuid (API boundary DTOs keep String for JSON)
- Auth middleware: parse JWT claims.sub (String) → Uuid at boundary
- All repository traits, port traits, service impls updated end-to-end
- Handlers: pass Uuid by value (Copy, 16 bytes) instead of String refs
- Settings chain: updated_by column → Uuid (was text, caused setup crash)
- Removed ~650 lines of String↔Uuid conversion boilerplate
- Eliminates per-request heap allocations for ID cloning
- 16-byte binary comparison vs 36-byte string comparison in all queries
- Native UUID indexing in PostgreSQL (btree on 16 bytes vs 36-char text)

85 files changed, 1090 insertions(+), 1739 deletions(-)

src/interfaces/nextcloud/preview_handler.rs

@@ -90,7 +90,8 @@ pub async fn handle_preview(
     };
 
     // Verify the authenticated user owns this file
-    if file.owner_id.as_deref() != Some(&user.id) {
+    let user_id_str = user.id.to_string();
+    if file.owner_id.as_deref() != Some(user_id_str.as_str()) {
         return Response::builder()
             .status(StatusCode::NOT_FOUND)
             .body(Body::from("File not found"))