Harden SimpleFin sync: retries, safer imports, manual relinking, and data-quality reconciliation (#544)

* Add tests and enhance logic for SimpleFin account synchronization and reconciliation

- Added retry logic with exponential backoff for network errors in `Provider::Simplefin`.
- Introduced tests to verify retry functionality and error handling for rate-limit, server errors, and stale data.
- Updated `SimplefinItem` to detect stale sync status and reconciliation issues.
- Enhanced UI to display stale sync warnings and data integrity notices.
- Improved SimpleFin account matching during updates with multi-tier strategy (ID, fingerprint, fuzzy match).
- Added transaction reconciliation logic to detect data gaps, transaction count drops, and duplicate transaction IDs.

* Introduce `SimplefinConnectionUpdateJob` for asynchronous SimpleFin connection updates

- Moved SimpleFin connection update logic to `SimplefinConnectionUpdateJob` to improve response times by offloading network retries, data fetching, and reconciliation tasks.
- Enhanced SimpleFin account matching with a multi-tier strategy (ID, fingerprint, fuzzy name match).
- Added retry logic and bounded latency for token claim requests in `Provider::Simplefin`.
- Updated tests to cover the new job flow and ensure correct account reconciliation during updates.

* Remove unused SimpleFin account matching logic and improve error handling in `SimplefinConnectionUpdateJob`

- Deleted the multi-tier account matching logic from `SimplefinItemsController` as it is no longer used.
- Enhanced error handling in `SimplefinConnectionUpdateJob` to gracefully handle import failures, ensuring orphaned items can be manually resolved.
- Updated job flow to conditionally set item status based on the success of import operations.

* Fix SimpleFin sync: check both legacy FK and AccountProvider for linked accounts

* Add crypto, checking, savings, and cash account detection; refine subtype selection and linking

- Enhanced `Simplefin::AccountTypeMapper` to include detection for crypto, checking, savings, and standalone cash accounts.
- Improved subtype selection UI with validation and warning indicators for missing selections.
- Updated SimpleFin account linking to handle both legacy FK and `AccountProvider` associations consistently.
- Refined job flow and importer logic for better handling of linked accounts and subtype inference.

* Improve `SimplefinConnectionUpdateJob` and holdings processing logic

- Fixed race condition in `SimplefinConnectionUpdateJob` by moving `destroy_later` calls outside of transactions.
- Updated fuzzy name match logic to use Levenshtein distance for better accuracy.
- Enhanced synthetic ticker generation in holdings processor with hash suffix for uniqueness.

* Refine SimpleFin entry processing logic and ensure `extra` data persistence

- Simplified pending flag determination to rely solely on provider-supplied values.
- Fixed potential stale values in `extra` by ensuring deep merge overwrite with `entry.transaction.save!`.

* Replace hardcoded fallback transaction description with localized string

* Refine pending flag logic in SimpleFin processor tests

- Adjust test to prevent falsely inferring pending status from missing posted dates.
- Ensure provider explicitly sets pending flag for transactions.

* Add `has_many :holdings` association to `AccountProvider` with `dependent: :nullify`

---------

Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>

test/models/simplefin_entry/processor_test.rb

@@ -53,7 +53,9 @@ class SimplefinEntry::ProcessorTest < ActiveSupport::TestCase
     assert_equal "Order #1234", sf["description"]
     assert_equal({ "category" => "restaurants", "check_number" => nil }, sf["extra"])
   end
-  test "flags pending transaction when posted is nil and transacted_at present" do
+  test "does not flag pending when posted is nil but provider pending flag not set" do
+    # Previously we inferred pending from missing posted date, but this was too aggressive -
+    # some providers don't supply posted dates even for settled transactions
     tx = {
       id: "tx_pending_1",
       amount: "-20.00",
@@ -70,7 +72,7 @@ class SimplefinEntry::ProcessorTest < ActiveSupport::TestCase
     entry = @account.entries.find_by!(external_id: "simplefin_tx_pending_1", source: "simplefin")
     sf = entry.transaction.extra.fetch("simplefin")
 
-    assert_equal true, sf["pending"], "expected pending flag to be true"
+    assert_equal false, sf["pending"], "expected pending flag to be false when provider doesn't explicitly set pending"
   end
 
   test "captures FX metadata when tx currency differs from account currency" do