deps(deps): bump alembic from 1.18.5 to 1.19.0 in /backend

[dependabot]

Bumps alembic from 1.18.5 to 1.19.0.

Release notes

Sourced from alembic's releases.

1.19.0

Released: August 4, 2026

changed

• [changed] [installation] Environmental updates:

  -   Trove classifiers now include Python 3.15 which is now part of CI
      integration
  
  
  Python 3.14 is also added to trove classifiers which had been previously
  omitted
  
  
  Implemented PEP 604 style unions in type annotations
  

feature

• [feature] [autogenerate] Autogenerate now detects the addition and removal of named CHECK constraints, as part of the default autogenerate behavior. Detection is name-based only; a constraint whose name is unchanged is presumed equivalent regardless of its expression text, as reliably normalizing SQL expressions across backends for comparison purposes is not generally feasible. This behavior is implemented as a plugin named alembic.autogenerate.checkconstraint_byname, and may be disabled if not desired by excluding it from the EnvironmentContext.configure.autogenerate_plugins list. Pull request courtesy Francois van Kempen.

  References: #508

bug

• [bug] [commands] Fixed inconsistency where running stamp or downgrade to base in offline (--sql) mode would emit a DROP TABLE alembic_version statement, while the same operations in online mode never drop the version table. Offline mode no longer emits this DROP, matching online behavior. The version table continues to be created when it does not exist; only the spurious offline-only drop has been removed. Pull request courtesy imurodl.

  References: #1822

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