Add Docker Compose for local development

[BigBen-7]

Description

One-command local setup.

Implementation

1. Create docker-compose.yml
2. Add Postgres + PostGIS
3. Add backend service

Complexity: 150 points

[NteinPrecious]

can i add the docker container to this project?

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #91)
2. Your PR will be reviewed by the PinSpace-Org maintainers

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