docs: add Step 10 rapidapi-proxy-secret to secrets-checklist.md

Add checklist item 10 and full detail section for the rapidapi-proxy-secret
Kubernetes secret that must be created in each API namespace (zip-enrichment,
holidays, air-quality) before the Phase 3 server middleware can validate
incoming RapidAPI requests.

Includes:
- Checklist item 10 in the summary list
- Full detail section with kubectl commands for all 3 namespaces
- Note about placeholder ExternalSecret manifests and ESO (issue #61)
- Updated dependency-order diagram

Closes leeworks-agents/api-company#60

docs/secrets-checklist.md

@@ -18,6 +18,7 @@ Follow this list top-to-bottom; each step unblocks the next.
 - [ ] 7. Add api-company Flux source + kustomization to 0xWheatyz/Talos — unblocks all GitOps reconciliation
 - [ ] 8. `gitea-registry` (zip-enrichment, holidays, air-quality, docs-site) — imagePullSecret for pods pulling from `registry.leeworks.dev`
 - [ ] 9. `gitea-image-automation-token` (flux-system) — write-scoped token for Flux ImageUpdateAutomation to push image-tag commits
+- [ ] 10. `rapidapi-proxy-secret` (zip-enrichment, holidays, air-quality) — RapidAPI Proxy Secret for server-side request validation
 
 ---
 
@@ -155,6 +156,44 @@ Unblocks: Issue #2 (Flux reconciliation of all `flux/` manifests in this repo).
 
 ---
 
+---
+
+### 10. `rapidapi-proxy-secret` — RapidAPI Proxy Secret (per API namespace)
+
+| Field     | Value |
+|-----------|-------|
+| Name      | `rapidapi-proxy-secret` |
+| Namespaces | `zip-enrichment`, `holidays`, `air-quality` |
+| Purpose   | Every API service validates the `X-RapidAPI-Proxy-Secret` header on every route. Requests without a valid secret return HTTP 403. |
+| Source    | RapidAPI dashboard → API Settings → Security → **Proxy Secret** (generated after each API listing is created) |
+| Unblocks  | Phase 3 server middleware; API services will start but reject all traffic without this secret |
+
+```bash
+for NS in zip-enrichment holidays air-quality; do
+  kubectl create secret generic rapidapi-proxy-secret \
+    --namespace=$NS \
+    --from-literal=X-RapidAPI-Proxy-Secret=<value-from-rapidapi-dashboard>
+done
+```
+
+**Source:** RapidAPI dashboard → select your API → Settings → Security → Proxy Secret
+
+> **Note:** Placeholder `ExternalSecret` manifests are committed at
+> `flux/zip-enrichment/externalsecret.yaml`, `flux/holidays/externalsecret.yaml`,
+> and `flux/air-quality/externalsecret.yaml`. These will auto-sync this secret
+> from the configured backend once the External Secrets Operator (ESO) is
+> deployed (see issue #61). Until then, create manually using the commands above.
+
+Verify:
+```bash
+for NS in zip-enrichment holidays air-quality; do
+  echo -n "$NS: "
+  kubectl get secret rapidapi-proxy-secret -n $NS -o jsonpath='{.data.X-RapidAPI-Proxy-Secret}' | base64 -d | wc -c
+  echo " chars"
+done
+```
+
+
 ## Dependency Order
 
 ```
@@ -166,6 +205,7 @@ Unblocks: Issue #2 (Flux reconciliation of all `flux/` manifests in this repo).
 5 + 6 (GITEA_TOKEN + registry packages) → CI pushes images → API services deploy
 8 (gitea-registry)       → pods can pull images from registry.leeworks.dev → services start
 9 (gitea-image-automation-token) → Flux ImageUpdateAutomation pushes tag-update commits
+10 (rapidapi-proxy-secret × 3)  → API server middleware validates RapidAPI requests → revenue enabled
 ```
 
 Once all nine items are complete, the full stack (runner, registry, Prometheus, Grafana, Gatus, docs-site, three API services) reconciles automatically via FluxCD with no further manual steps.