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/domain/repositories/settings_repository.rs

@@ -1,5 +1,6 @@
 use crate::common::errors::DomainError;
 use std::collections::HashMap;
+use uuid::Uuid;
 
 /// Repository for platform settings stored in the database.
 /// Settings are key-value pairs organized by category (e.g., "oidc", "general").
@@ -18,7 +19,7 @@ pub trait SettingsRepository: Send + Sync + 'static {
         value: &str,
         category: &str,
         is_secret: bool,
-        updated_by: Option<&str>,
+        updated_by: Option<Uuid>,
     ) -> Result<(), DomainError>;
 
     /// Delete a setting by key
@@ -34,7 +35,7 @@ pub trait SettingsRepository: Send + Sync + 'static {
     /// The default implementation falls back to the non-atomic
     /// get-then-set pattern for repositories that don't support a native
     /// atomic upsert.
-    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> {
         // Default: non-atomic fallback (overridden by PG implementation)
         match self.get("system_initialized").await? {
             Some(v) if v == "true" => Ok(false),