fix: harden engine, enrich failure diagnostics, close adoption gaps

- P0: CLI verify now honors  test budget with seeded multi-sample
- P0: Observe sampling enforced via Math.random() gate in hook-validator
- P1: Remove misleading undici-mock-agent isolation option
- P1: Qualify reuses shared discoverRouteDetails() with warnings
- P1: Chaos/scenario config exposed via preset schema
- P1: README/docs limitations updated to current state
- P2: Nested response annotations prefer 2xx deterministically
- P2: --changed documented as heuristic in verify.md

- Add observe sink tests (sampling 0/1, sink failure non-interference)
- Add verify runs regression tests (scale, determinism, variants)
- Add configured-scenario qualify test (independent of OAuth fixture)
- Add coverageBreakdown to qualify artifacts (per-gate route coverage)
- Add production-style observe example with real sink in docs/observe.md
- Add nightly/staging vs PR gating guidance to docs/qualify.md

- Enrich VerifyFailure with formula-aware diagnostics:
  status:201 => 'HTTP 200', body field checks => actual values
- Remove stale observe CLI activation message
- Document outbound mocks as process-global in getting-started.md
- Refresh APOPHIS_ADOPTION_AUDIT.md with current state

903 tests pass, build clean, typecheck clean.

docs/attic/fastify-structure.md

@@ -202,7 +202,7 @@ The production entry point imports the app factory, adds APOPHIS, connects to se
 
 ```typescript
 import { buildApp } from './app'
-import apophis from 'apophis-fastify'
+import apophis from '@apophis/fastify'
 
 async function start() {
   const fastify = await buildApp({
@@ -236,7 +236,7 @@ The test file creates a fresh app instance, registers APOPHIS, and runs contract
 
 ```typescript
 import { buildApp } from '../app'
-import apophis from 'apophis-fastify'
+import apophis from '@apophis/fastify'
 import type { FastifyInstance } from 'fastify'
 
 export async function createTestApp(): Promise<FastifyInstance> {