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/infrastructure/repositories/pg/settings_pg_repository.rs

@@ -1,6 +1,7 @@
 use sqlx::PgPool;
 use std::collections::HashMap;
 use std::sync::Arc;
+use uuid::Uuid;
 
 use crate::common::errors::{DomainError, ErrorKind};
 use crate::domain::repositories::settings_repository::SettingsRepository;
@@ -60,7 +61,7 @@ impl SettingsRepository for SettingsPgRepository {
         value: &str,
         category: &str,
         is_secret: bool,
-        updated_by: Option<&str>,
+        updated_by: Option<Uuid>,
     ) -> Result<(), DomainError> {
         sqlx::query(
             "INSERT INTO auth.admin_settings (key, value, category, is_secret, updated_by, updated_at)
@@ -102,7 +103,7 @@ impl SettingsRepository for SettingsPgRepository {
     ///
     /// Only the first caller that inserts the row gets `rows_affected == 1`;
     /// concurrent callers see 0 rows affected and receive `false`.
-    async fn try_claim_initialization(&self, admin_user_id: &str) -> Result<bool, DomainError> {
+    async fn try_claim_initialization(&self, admin_user_id: Uuid) -> Result<bool, DomainError> {
         let result = sqlx::query(
             "INSERT INTO auth.admin_settings (key, value, category, is_secret, updated_by, updated_at)
              VALUES ('system_initialized', 'true', 'system', false, $1, NOW())