fix: postgres 18 compatibility + root docker-compose + ETL-tuned pg config

[Copilot]

Three related issues with the Docker/Compose setup: PG18 breaks on wal_level=minimal without max_wal_senders=0, PG18 changed the expected volume mount path, and there was no compose file for running the production app end-to-end.

PostgreSQL 18 breaking changes (both compose files)

• max_wal_senders default changed 0→10 in PG18 — setting wal_level=minimal now requires explicitly adding -c max_wal_senders=0, otherwise PG crashes on startup:

  FATAL: WAL streaming ("max_wal_senders" > 0) requires "wal_level" to be "replica" or "logical"
  

• Volume mount path changed — PG18 manages its own versioned subdirectory (18/main) and expects the volume at /var/lib/postgresql, not /var/lib/postgresql/data

ETL-optimised postgres config

Tuned for the bulk GitHub API → star-schema upsert workload (both compose files):

Setting	Value	Rationale
shared_buffers	256MB	Dimension table cache hits during repeated upserts
work_mem	16MB	Avoids disk spill per upsert hash-join/sort op
maintenance_work_mem	64MB	Faster index rebuilds post bulk-insert batch
effective_cache_size	512MB	Planner prefers index scans on dimension tables
max_wal_size	512MB	Caps WAL between checkpoints
checkpoint_timeout	15min	Prevents mid-import checkpoint stalls
default_statistics_target	200	Better post-ANALYZE plans on skewed dims
shm_size	512m	Matches shared_buffers

New root docker-compose.yml

Adds a compose file for running the full production stack locally (previously only the devcontainer compose existed, which runs sleep infinity):

docker compose up --build   # builds app/Dockerfile, starts PG, opens :3000

ADMIN_PASSWORD defaults to changeme123 — override via .env or environment variable before use.

[Copilot]

Pull request overview

Adds Postgres 18 compatibility fixes and a new root Compose setup to run the app + database locally, with Postgres settings tuned for the ETL/upsert workload.

Changes:

• Added a root docker-compose.yml to build/run the production Docker image alongside Postgres.
• Updated Postgres 18 Compose settings (volume mount path + max_wal_senders=0 with wal_level=minimal) and applied ETL-oriented Postgres tuning in both compose files.
• Simplified .devcontainer/docker-compose.yml by removing deploy.resources and wiring services onto an explicit network.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docker-compose.yml	New end-to-end local Compose stack (app + Postgres 18) with ETL-tuned Postgres config and healthchecks.
.devcontainer/docker-compose.yml	Aligns devcontainer Postgres 18 config and healthcheck with the new tuning/compatibility requirements; adds explicit devnet network.