Add SnapTrade brokerage integration with full trade history support (#737)

* Introduce SnapTrade integration with models, migrations, views, and activity processing logic.

* Refactor SnapTrade activities processing: improve activity fetching flow, handle pending states, and update UI elements for enhanced user feedback.

* Update Brakeman ignore file to include intentional redirect for SnapTrade OAuth portal.

* Refactor SnapTrade models, views, and processing logic: add currency extraction helper, improve pending state handling, optimize migration checks, and enhance user feedback in UI.

* Remove encryption for SnapTrade `snaptrade_user_id`, as it is an identifier, not a secret.

* Introduce `SnaptradeConnectionCleanupJob` to asynchronously handle SnapTrade connection cleanup and improve i18n for SnapTrade item status messages.

* Update SnapTrade encryption: make `snaptrade_user_secret` non-deterministic to enhance security.

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Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>
Co-authored-by: luckyPipewrench <luckypipewrench@proton.me>
Co-authored-by: Juan José Mata <juanjo.mata@gmail.com>

test/fixtures/snaptrade_items.yml

@@ -0,0 +1,20 @@
+# Minimal fixtures for SnapTrade items
+# Per CLAUDE.md: Keep fixtures minimal (2-3 per model for base cases)
+
+configured_item:
+  family: dylan_family
+  name: "SnapTrade Connection"
+  client_id: "test_client_id"
+  consumer_key: "test_consumer_key"
+  snaptrade_user_id: "user_123"
+  snaptrade_user_secret: "secret_abc"
+  status: good
+  scheduled_for_deletion: false
+  pending_account_setup: false
+
+unconfigured_item:
+  family: empty
+  name: "Pending Setup"
+  status: good
+  scheduled_for_deletion: false
+  pending_account_setup: true