Migrate configuration from JSON to TOML (closes #58)

[SimmerV]

Summary

• Added config.toml.sample as the new primary config format, using Python's built-in tomllib (no new dependencies)
• Updated config.py to load config.toml first with automatic fallback to config.json + deprecation warning
• Updated Docker volume mounts, backup logic, migration script, .gitignore, tests, and docs (README, POSTGRES.md)

Notes

• Existing config.json deployments continue to work — they'll see a deprecation warning in logs

[Copilot]

Pull request overview

Migrates MeshInfo’s primary configuration format from JSON to TOML while preserving legacy config.json support via fallback loading and deprecation warnings.

Changes:

• Added config.toml.sample and updated tests to validate the new sample while keeping config.json.sample valid.
• Updated Config.load() to prefer config.toml, fall back to config.json with a deprecation warning, and adjusted related error/help messaging.
• Updated Docker compose mounts, backup behavior, migration-script messaging, .gitignore, and docs to reference TOML.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
config.py	Implements TOML-first config loading with JSON fallback and updates related messaging/helpers.
config.toml.sample	Adds the canonical sample configuration in TOML format.
docker-compose.yml	Mounts config.toml into the container instead of config.json.
docker-compose-dev.yml	Mounts config.toml into the dev container instead of config.json.
memory_data_store.py	Updates backup routine to include config.toml when present (else config.json).
scripts/migrate_json_to_postgres.py	Updates user-facing log messages to reflect TOML/JSON config support.
tests/test_config_sample_is_valid_json.py	Adds TOML sample validation and keeps legacy JSON sample validation.
tests/test_assets_present.py	Ensures config.toml.sample is treated as a required repo asset.
README.md	Updates setup instructions to prefer TOML (with legacy JSON mention).
POSTGRES.md	Updates PostgreSQL configuration examples/instructions to TOML.
.gitignore	Ignores config.toml in addition to config.json.

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