Support composable SOP configs (extends/imports)

[ldraney]

Context

As teams adopt dev-sop-engine, they'll want to share and layer configurations — e.g., a company base config with project-specific overrides. This is the pattern that made ESLint, Prettier, and TSConfig widely adopted.

Proposal

Add an extends field to sop.json:

{
  "extends": "@company/base-sop",  // npm package or relative path
  "rules": {
    "no-env-writes": { "enabled": false }  // Override inherited rule
  }
}

Semantics to decide

• Merge strategy: deep merge? Per-section override? Array concat for events?
• Resolution: npm packages? Git URLs? Local paths only?
• Conflict handling: last-writer-wins? Explicit error on collision?

Why it matters

This is the difference between a tool individuals use and a tool organizations adopt. Shared, composable configs are the standard pattern for dev tooling governance.