fix: document and consolidate DB_* env vars for knexfile

[amujapromise9-dev]

Overview

This PR fixes the undocumented DB_* environment variables in src/knexfile.ts by adding DB_HOST, DB_PORT, DB_NAME, DB_USER, and DB_PASSWORD to .env.example and docs/SETUP.md, and routing them through src/config.ts — the codebase's single module for environment configuration. This makes the migration system's Postgres connection settings visible, configurable, and consistent with every other environment variable in the app.

Related Issue

Closes #

Changes

📝 Environment Variable Documentation

• [ADD] .env.example

  • Adds DB_HOST, DB_PORT, DB_NAME, DB_USER, and DB_PASSWORD with sensible defaults/placeholders for local Postgres development.

• [ADD] docs/SETUP.md

  • Adds the five DB_* variables to the "Environment Variables Reference" table with descriptions and example values.

🔧 Config Consolidation

• [MODIFY] src/config.ts

  • Adds DB_HOST, DB_PORT, DB_NAME, DB_USER, and DB_PASSWORD fields to the config object, following the existing pattern used by PORT, RPC_URL, etc.

• [MODIFY] src/knexfile.ts

  • Replaces direct process.env.DB_* reads with the consolidated config module, so all environment configuration flows through a single source of truth.

Verification Results

$ grep -n "DB_HOST\|DB_PORT\|DB_NAME\|DB_USER\|DB_PASSWORD" .env.example src/config.ts docs/SETUP.md
✅ All five DB_* vars now present in all three files

$ npm test
✅ 64/64 passed

Acceptance Criteria	Status
DB_HOST/DB_PORT/DB_NAME/DB_USER/DB_PASSWORD documented in .env.example	✅ Added with sensible defaults/placeholders
DB_* variables added to docs/SETUP.md environment variable table	✅ Documented with descriptions and example values
DB_* variables routed through src/config.ts	✅ Config exports db settings; knexfile.ts consumes them
Migration system behavior unchanged	✅ getKnexInstance() produces identical Postgres config from consolidated source

Closes #465

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