chore: replace docker-compose with nix process-compose for dev deps

[Lakshyyaa]

Follows GaloyMoney/es-entity#140. Migrates job's dev loop off Docker/podman onto a Nix-managed process-compose Postgres, with per-worktree port allocation so multiple checkouts run their dev DB in parallel. No Docker required for sqlx-prepare, integration tests, or make start-deps.

Changes

• flake.nix: add process-compose-flake input; dev-env (CRC32-of-cwd → dynamic PGPORT), pg-start (root setpriv drop + bounded readiness), setup-db-dev, mkPg/nix-deps-base; rewrite nextest-runner (XDG_CONFIG_HOME, _pgdev, bounded readiness wait, synchronous migrations); drop docker-compose/podman/podman-compose, add process-compose; export dev-env/setup-db-dev/nix-deps-base packages+apps; devShell shellHook evals dev-env
• Makefile: start-deps/clean-deps/setup-db/reset-deps via process-compose + bounded wait; migrations folded into start-deps
• tests/helpers.rs: read PG_CON from env (dynamic port) instead of hardcoded :5432
• ci/pipeline.yml: drop privileged: true (no container engine needed in CI)
• remove docker-compose.yml, nix/podman-runner.nix
• .gitignore: add .nix-deps/

Notes

• SQLX_OFFLINE=true stays in commonArgs (crane nix flake check builds offline against .sqlx/). The nextest-runner compiles online against the live migrated PG — mirrors es-entity#140 and adds schema-drift coverage the offline checks can't.
• Supersedes the stale chore/nix-process-compose-dev-deps branch, which used a static :5432 port (didn't solve multi-worktree).

Verification

• alejandra -c flake.nix ✅
• nix run .#dev-env → consistent per-worktree derivation (PGPORT=25200, matching PG_CON) ✅
• make start-deps → PG up via process-compose on derived port, migrations applied ✅
• cargo nextest run --workspace → 58 passed, 0 failed ✅
• make clean-deps → torn down ✅

🤖 Generated with Claude Code

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Note

Medium Risk
Touches CI test bootstrap, dev workflows, and test DB connectivity; behavior change is intentional but broad across local and CI paths.

Overview
Replaces Docker/podman-compose dev Postgres with Nix process-compose and a local pg-start helper under .nix-deps/, so make start-deps, sqlx-prepare, and integration tests no longer need a container engine.

Adds dev-env (CRC32 of checkout path → dynamic PGPORT / PG_CON) so multiple worktrees can run Postgres in parallel, plus setup-db-dev and nix-deps-base with bounded readiness waits; Makefile targets now start/stop deps via nix run and run migrations after Postgres is healthy. nextest-runner and the dev shell follow the same flow (including root setpriv drop to UID 70 in CI). Integration tests read PG_CON from the environment instead of a fixed :5432 host. CI drops privileged: true on the tests job. Removes docker-compose.yml, nix/podman-runner.nix, and ignores .nix-deps/.

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