#523 - Centralize and type environment configuration

[brijesh-amin]

Parent: #523

Objective

Create a single validated env/config surface to prevent late runtime failures and inconsistent module-level env access.

In scope

• Introduce centralized env schema validation (required vars + type coercion)
• Export typed config consumed by runtime modules
• Migrate selected modules from direct process.env reads to typed config

Acceptance criteria

• Startup fails fast with actionable errors when required env vars are missing/invalid
• Typed config object is the primary read path in touched modules
• Reduced ad-hoc env access in updated areas
• Tests cover invalid/missing env behavior

Notes

Adopt incrementally to minimize merge conflict risk.