docs: add scenario examples, fix sampling docs, improve pedagogical completeness

- Add actual scenario definition example to qualify.md
- Add stateful test API example to qualify.md
- Fix observe.md sampling section to show explicit config and rates
- Build: clean | Tests: 849 pass, 0 fail

docs/observe.md

@@ -67,7 +67,18 @@ profiles: {
 }
 ```
 
-The `platform-observe` preset enables sampling at the preset level.
+The `platform-observe` preset enables sampling. Configure the rate explicitly:
+
+```javascript
+profiles: {
+  'staging-observe': {
+    mode: 'observe',
+    preset: 'platform-observe',
+    routes: [],
+    sampling: 1.0  // 100% of requests observed
+  }
+}
+```
 
 ## Staging vs Production
 
@@ -76,7 +87,18 @@ The `platform-observe` preset enables sampling at the preset level.
 | Staging | No (default) | 100% | Yes |
 | Production | No (default) | 100% | Yes |
 
-Default is 1.0 (100%). Configure lower rates for production explicitly.
+Default is `1.0` (100%). Configure lower rates for production explicitly:
+
+```javascript
+profiles: {
+  'prod-observe': {
+    mode: 'observe',
+    preset: 'platform-observe',
+    routes: [],
+    sampling: 0.1  // 10% of requests observed
+  }
+}
+```
 
 ## `--check-config` Flag