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/root-history/DX_IMPROVEMENT_PLAN.md

@@ -12,14 +12,14 @@ A complete "Hello World" to "Production Ready" guide that a developer can follow
 
 #### 1.1 Installation (30 seconds)
 ```bash
-npm install apophis-fastify
+npm install @apophis/fastify
 # peer deps: fastify, @fastify/swagger
 ```
 
 #### 1.2 Minimal Setup (2 minutes)
 ```typescript
 import Fastify from 'fastify'
-import apophisPlugin from 'apophis-fastify'
+import apophisPlugin from '@apophis/fastify'
 
 const fastify = Fastify()
 
@@ -358,7 +358,7 @@ jobs:
 #### 3.4 Cache Configuration API
 ```typescript
 // Programmatic control
-import { invalidateRoutes, invalidateCache } from 'apophis-fastify/incremental/cache'
+import { invalidateRoutes, invalidateCache } from '@apophis/fastify/incremental/cache'
 
 // Before test run
 invalidateRoutes(['/users'])  // Invalidate specific routes