Qualify updated_at in document filters to avoid ambiguous column

[vswamidass-sfdc]

Problem

The documents index (BaseDocumentsController#index) 500s with PG::AmbiguousColumn: column reference "updated_at" is ambiguous when a since/until date filter is combined with a similarity search whose results are materialized.

The index eager-loads :library and :user. When those associations get forced into the query as LEFT OUTER JOINs (e.g. when similarity results are materialized via pluck), the bare where('updated_at > ?') filter becomes ambiguous — documents, libraries, and users all have an updated_at column.

Fix

Qualify the column as documents.updated_at in both the since and until branches.

Tests

Added test/models/document_similarity_filter_test.rb, which reproduces the exact failing query shape (eager-loaded associations + updated_at filter + materialization):

• Confirms the qualified filter runs cleanly.
• Confirms the unqualified filter raises PG::AmbiguousColumn — so this is a real regression guard, not a no-op.

Incidental

The api_tokens fixture was empty ({}) while the schema requires a non-null user_id, which caused fixtures :all to fail and blocked the entire test suite from loading. Populated it minimally so tests can run.

Note

On main today this bug is latent: the controller's similar_to path is lazy, so includes runs as separate preload queries with no JOIN, and the ambiguity isn't reachable through a normal request. The JOIN (and the crash) appears once similarity results are materialized. The qualified-column fix is correct regardless and prevents the latent bug from surfacing.