feat: extend Flux image automation, Gatus, and docs for VIN Decoder

Closes leeworks-agents/api-company#133
Closes leeworks-agents/api-company#134
Closes leeworks-agents/api-company#135
Closes leeworks-agents/api-company#136

- flux/image-automation/imagerepositories.yaml: add vin-decoder ImageRepository
  pointing at registry.leeworks.dev/vin-decoder/api (#133)
- flux/image-automation/imagepolicies.yaml: add vin-decoder ImagePolicy
  with semver range >=0.1.0 (#133)
- flux/monitoring/gatus-helmrelease.yaml: add VIN Decoder API endpoint check
  targeting https://vin.leeworks.dev/v1/health with Slack alert (#134)
- docs/pre-launch-checklist.md: add vin-decoder to Infrastructure, DNS & TLS,
  Functional Verification, and Legal sections; update status page line to
  reference all four APIs (#135)
- docs/secrets-checklist.md: add items #11-13 for vin-decoder GITEA_TOKEN,
  gitea-registry, and rapidapi-proxy-secret; add detail sections for each (#136)

kustomize build flux/ passes with zero errors.

flux/image-automation/imagepolicies.yaml

@@ -40,6 +40,18 @@ spec:
 ---
 apiVersion: image.toolkit.fluxcd.io/v1beta2
 kind: ImagePolicy
+metadata:
+  name: vin-decoder
+  namespace: flux-system
+spec:
+  imageRepositoryRef:
+    name: vin-decoder
+  policy:
+    semver:
+      range: ">=0.1.0"
+---
+apiVersion: image.toolkit.fluxcd.io/v1beta2
+kind: ImagePolicy
 metadata:
   name: docs-site
   namespace: flux-system