chore: backport process-compose follow-up fixes from cala

[Lakshyyaa]

What

cala#729 ported the nix process-compose dev-deps setup from es-entity #140. During its review, two follow-up bugs were found and fixed in cala that originate in the shared pattern but were never backported here. This PR brings es-entity to parity.

Fixes

1. flake.nix — always derive DATABASE_URL from PGPORT

es-entity-dev-env derives a per-worktree PGPORT from a CRC32 of the checkout path, but built DATABASE_URL via ${DATABASE_URL:-...} — honoring any pre-set value. That made the URL an independent input that could disagree with the hash-derived port: a stale DATABASE_URL (e.g. a :5432 export from direnv dotenv) keeps the old port while Postgres binds PGPORT, so clients/migrations hit the wrong port → drift.

Drop the :- guard so the URL is always derived from PGPORT. Port = single source of truth, URL = output. PGPORT itself stays overridable. (cala 4041bb2)

2. Makefile — set -e in start-deps

Without set -e, a failed nix-deps-base up -D (PC port busy, bad config) falls through to the readiness loop and only errors after the full 5-minute timeout. set -e aborts immediately, matching nextest-runner which already wraps its deps-up flow in set -e. The readiness loop is unaffected: is-ready runs in an if-condition and process list || true is guarded. (cala 496fd1b)

Notes / not included

• cala's other commits were cala-specific (es-entity version bump, docker-file removal, examples/rust/cala-ledger doctest → PG_CON) or already present here (per-worktree dynamic port, kill -0 liveness guard, bounded readiness wait, book examples already read PG_CON).
• cala dropped SQLX_OFFLINE=true from its test runner to validate queries online — es-entity's nextest-runner never set it, so no change needed.
• cala removed a dead test-in-ci Make target because its helpers .unwrap() PG_CON without starting deps. es-entity's test-in-ci has start-deps as a prereq so it isn't broken; left in place (CI uses nix run .#nextest, so it is unused — worth a separate cleanup if desired).

🤖 Generated with Claude Code

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Note

Low Risk
Local/CI dev tooling and documentation only; no application runtime, auth, or persistence logic changes.

Overview
Backports two dev-deps fixes from the shared process-compose pattern: DATABASE_URL is always computed from the hash-derived PGPORT in es-entity-dev-env (no longer honoring a pre-set DATABASE_URL), so a stale env export cannot point clients at the wrong port while Postgres listens on PGPORT.

make start-deps now runs under set -e, so a failed nix-deps-base up -D fails immediately instead of waiting through the full readiness timeout.

Docs clarify SQLX_OFFLINE: offline .sqlx/ validation in nix flake check vs live DB for nix run .#nextest. The unused test-in-ci Make target is removed from .PHONY and the Makefile (CI uses nix run .#nextest).

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