feat(05-01): extend VerifySpec and Finding, add gjson dep

- VerifySpec: add SuccessCodes, FailureCodes, RateLimitCodes, MetadataPaths, Body
- Preserve legacy ValidStatus/InvalidStatus for backward compat
- Add EffectiveSuccessCodes/FailureCodes/RateLimitCodes fallback helpers
- Add ExtractMetadata helper using gjson (skeleton for Plan 05-03)
- Finding: add Verified, VerifyStatus, VerifyHTTPCode, VerifyMetadata, VerifyError
- Add github.com/tidwall/gjson v1.18.0 as direct dependency

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
 	github.com/stretchr/testify v1.11.1
+	github.com/tidwall/gjson v1.18.0
 	golang.org/x/crypto v0.49.0
 	golang.org/x/exp v0.0.0-20260312153236-7ab1446f8b90
 	golang.org/x/time v0.15.0
@@ -59,6 +60,8 @@ require (
 	github.com/spf13/cast v1.10.0 // indirect
 	github.com/spf13/pflag v1.0.10 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.0 // indirect
 	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect