feat(storage): default to SQLite

[ArionMiles]

Description

Add SQLite as the default storage backend for fresh installations while retaining PostgreSQL as an explicit option. Production builds now embed the frontend and ship as one container or native binary.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Build/CI configuration change

Related Issue

No linked issue.

Changes Made

• Add a complete SQLite store with secure local-file handling, migrations, conformance tests, and PostgreSQL behavior parity.
• Embed the production UI and add SQLite-first Docker Compose, native archives, checksum verification, and a POSIX installer.
• Update CI, release automation, smoke tests, and documentation for SQLite defaults and PostgreSQL opt-in.

Testing

• Unit tests pass (task test:be)
• Linter passes (task lint:be:prod and task lint:fe)
• Manual testing completed
• Added new tests (if applicable)

Additional validation includes SQLite race tests, PostgreSQL integration tests, dependency audits, OpenAPI drift checks, Compose checks, archive and installer tests, Docker smoke tests, native archive smoke tests, and workflow lint. Frontend checks ran in Docker because Node and npm are not installed on the host.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable.

Additional Notes

Existing PostgreSQL deployments must select the PostgreSQL backend explicitly. The PostgreSQL Compose definition is now deploy/docker-compose.postgres.yml.