feat(settings): add model provider management with full CRUD support

Add a new settings page for managing API model providers (name, API URL,
API key, applicable agent types). Includes database migration, SeaORM
entity, backend CRUD commands/handlers, frontend settings UI with agent
type filter, add/edit/delete dialogs, and i18n support for all 10 locales.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/db/migration/m20260404_000001_model_provider.rs

@@ -0,0 +1,61 @@
+use sea_orm_migration::prelude::*;
+
+#[derive(DeriveMigrationName)]
+pub struct Migration;
+
+#[async_trait::async_trait]
+impl MigrationTrait for Migration {
+    async fn up(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        manager
+            .create_table(
+                Table::create()
+                    .table(ModelProvider::Table)
+                    .if_not_exists()
+                    .col(
+                        ColumnDef::new(ModelProvider::Id)
+                            .integer()
+                            .not_null()
+                            .auto_increment()
+                            .primary_key(),
+                    )
+                    .col(ColumnDef::new(ModelProvider::Name).string().not_null())
+                    .col(ColumnDef::new(ModelProvider::ApiUrl).text().not_null())
+                    .col(ColumnDef::new(ModelProvider::ApiKey).text().not_null())
+                    .col(
+                        ColumnDef::new(ModelProvider::AgentTypesJson)
+                            .text()
+                            .not_null(),
+                    )
+                    .col(
+                        ColumnDef::new(ModelProvider::CreatedAt)
+                            .timestamp_with_time_zone()
+                            .not_null(),
+                    )
+                    .col(
+                        ColumnDef::new(ModelProvider::UpdatedAt)
+                            .timestamp_with_time_zone()
+                            .not_null(),
+                    )
+                    .to_owned(),
+            )
+            .await
+    }
+
+    async fn down(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        manager
+            .drop_table(Table::drop().table(ModelProvider::Table).to_owned())
+            .await
+    }
+}
+
+#[derive(DeriveIden)]
+enum ModelProvider {
+    Table,
+    Id,
+    Name,
+    ApiUrl,
+    ApiKey,
+    AgentTypesJson,
+    CreatedAt,
+    UpdatedAt,
+}

src-tauri/src/db/migration/mod.rs

@@ -7,6 +7,7 @@ mod m20260226_000001_agent_setting;
 mod m20260227_000001_folder_parent_branch;
 mod m20260330_000001_chat_channel;
 mod m20260401_000001_chat_channel_sender_context;
+mod m20260404_000001_model_provider;
 pub struct Migrator;
 
 #[async_trait::async_trait]
@@ -20,6 +21,7 @@ impl MigratorTrait for Migrator {
             Box::new(m20260227_000001_folder_parent_branch::Migration),
             Box::new(m20260330_000001_chat_channel::Migration),
             Box::new(m20260401_000001_chat_channel_sender_context::Migration),
+            Box::new(m20260404_000001_model_provider::Migration),
         ]
     }
 }