fix(docker): pin postgres image and use named volume

[CKodidela]

Description

This PR updates docker-compose.yml to stabilize the local development environment across different operating systems by preventing two common database crash scenarios:

1. Pinned PostgreSQL Image (postgres:14): Prevents Docker from pulling newer major versions (like v18), which crash on startup when attempting to read .nostr/data files created by older versions.
2. Migrated to Named Docker Volume: Switched the local DB file mapping from a bound path (${PWD}/.nostr/data) to a standard named Docker volume (nostream-db-data). This resolves persistent file permission errors (Operation not permitted on initdb) encountered by developers running Docker Desktop via Windows/WSL.

Related Issue

Fixes #387

Motivation and Context

Running ./scripts/start_local can easily result in immediate failure for new contributors or developers returning after a while depending on their OS or caching status. By pinning the DB version and using proper Docker volumes for data mounts, the spin-up process becomes completely deterministic and avoids brittle Linux-to-WSL file system boundaries.

How Has This Been Tested?

• Verified that deleting existing containers/volumes and running ./scripts/start_local correctly provisions PostgreSQL 14 and initializes the data directory.
• Confirmed nostream-db container reaches a healthy state, allowing the rest of the application (Redis, migrations, web socket server) to boot without looping/crashing.
• Tested locally on Windows via WSL to ensure filesystem permission errors are bypassed entirely.

Screenshots (if appropriate):

Types of changes

• Non-functional change (docs, style, minor refactor)
• 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 change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• All new and existing tests passed.

[CKodidela]

Hey! I noticed the 'Files changed' diff shows changes across the entire docker-compose.yml instead of just the 3 lines I edited. It looks like my code editor's auto-formatter ran on save and cleaned up the indentation/quotes globally before I committed. I apologize for the noise in the diff! I've disabled my auto-formatter for this workspace and will be more careful with it off from here out in future commits going forward.

[cameri]

this is a breaking change for anyone currently using Nostream. Can you elaborate why you think this is necessary?