Bump alembic from 1.17.1 to 1.18.5 in /app/backend

[dependabot]

Bumps alembic from 1.17.1 to 1.18.5.

Release notes

Sourced from alembic's releases.

1.18.5

Released: June 25, 2026

usecase

• [usecase] [commands] Added --splice support to the merge() command. Previously, the merge command would suggest using --splice when attempting to merge non-head revisions, but the flag was not actually accepted by the command. The splice parameter is now available in both the command-line interface and the command.merge() function, matching the existing support in command.revision(). Pull request courtesy Kadir Can Ozden.

  References: #1712

• [usecase] [environment] Added ScriptDirectory.get_heads.consider_depends_on parameter to ScriptDirectory.get_heads(). When set to True, head revisions that are also a dependency of another revision via depends_on are excluded from the result, matching the effective heads that would be present in the alembic_version table after running all upgrades.

  References: #1806

bug

• [bug] [autogenerate] Fixed rendering of dialect keyword arguments containing ~sqlalchemy.schema.Column objects within sequences, such as postgresql_include. These were previously rendered using repr(), producing invalid Python in the generated migration scripts. Column objects within list or tuple values are now correctly rendered as their string column names. Pull request courtesy Ajay Singh.

  References: #1258

• [bug] [mysql] Implemented type comparison for ENUM datatypes on MySQL, which checks that the individual enum values are equivalent. If additional entries are on either side, this generates a diff. Changes of order do not generate a diff. Pull request courtesy Furkan Köykıran.

  References: #1745, #779

• [bug] [operations] Fixed bug where the inline_references parameter of Operations.add_column() did not include foreign key referential actions such as ON DELETE, ON UPDATE, DEFERRABLE, INITIALLY, and MATCH when rendering the inline REFERENCES clause.

... (truncated)

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[github-actions]

📝 Release Notes

This PR does not need to be included in release notes.

Reason: This PR is a routine dependency update for Alembic with no direct user-facing changes and no evidence of a significant platform reliability, performance, or infrastructure improvement that end users would notice.

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: exclude
Reasoning: This PR is a routine dependency update for Alembic with no direct user-facing changes and no evidence of a significant platform reliability, performance, or infrastructure improvement that end users would notice.