docs: separate detailed single-region onboarding from technical reference

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Hou Chi Chan

README.md

@@ -1,6 +1,8 @@
-# EPP Onboarding
+# EPP Detailed Configuration and Validation
 
-Follow these five steps for the External Phone Provider (EPP) Function. Choose one language:
+For first-time single-region deployment, start with the [main onboarding guide](../README.md).
+This guide covers detailed configuration, local development, and validation of the External Phone
+Provider (EPP) Function. Choose one language:
 [JavaScript](../javascript/README.md), [Python](../python/README.md), or [.NET](../dotnet/README.md).
 Use [CONTRACT.md](CONTRACT.md) for the full request contract and production limitations.
 
@@ -123,8 +125,8 @@ Use [CONTRACT.md](CONTRACT.md) for the full request contract and production limi
 	 change signing keys; request a fresh token afterward. This does **not** disable the required
 	 JWE encryption of `encryptedDeliveryContext` or remove `EPP_DECRYPTION_KEY_PEM`.
 
-	 Download the selected language's [Function ZIP](../README.md#download-a-function-zip) from GitHub
-	 Releases, or use the [root-level packaging scripts](../README.md#build-zips-locally) for custom builds.
+	 Download the selected language's [Function ZIP](../TECHNICAL.md#download-a-function-zip) from GitHub
+	 Releases, or use the [root-level packaging scripts](../TECHNICAL.md#build-zips-locally) for custom builds.
 	 The .NET source ZIP must be extracted and built/published with the .NET 8 SDK or a build-enabled
 	 deployment pipeline. The Python source ZIP requires Azure remote build on Linux. Neither source
 	 ZIP is ready for direct run-from-package. Downloading or building a ZIP does not deploy it.

TECHNICAL.md

@@ -55,7 +55,7 @@ matching provider authentication settings to `Values`.
 Add `EPP_PROVIDER_ACCOUNT_NAME` and adapter-specific options only when required. Optional
 `EPP_PROVIDER_TIMEOUT_MS` is a string such as `"1500"`. Replace placeholders; store provider credentials
 under the adapter's Key Vault secret names, not in local settings. See the
-[complete variable table](../README.md#configure-environment-variables).
+[complete variable table](../TECHNICAL.md#configure-environment-variables).
 
 Core Tools loads `Values` into environment variables. [AppConfig.Read](Src/AppConfig.cs) reads them
 through `IEnv`; direct worker execution and unit tests do not automatically load local settings.

docs/ONBOARDING.md

@@ -50,7 +50,7 @@ For live delivery, add `EPP_PROVIDER_NAME`, the complete selected `EPP_PROVIDER_
 matching provider authentication settings to `Values`.
 Add `EPP_PROVIDER_ACCOUNT_NAME` and any adapter-specific options only when required. Optional
 `EPP_PROVIDER_TIMEOUT_MS` is a string such as `"1500"`. Replace placeholders; do not put API keys in
-this file. See the [complete variable table](../README.md#configure-environment-variables).
+this file. See the [complete variable table](../TECHNICAL.md#configure-environment-variables).
 
 Core Tools copies `Values` into the process environment; direct Node processes and the offline tests
 do **not** automatically load this file. [AppConfig](src/functions/config.js) reads `process.env`

docs/images/single-region-architecture.png

@@ -50,7 +50,7 @@ matching provider authentication settings to `Values`.
 Add `EPP_PROVIDER_ACCOUNT_NAME` and any adapter-specific options only when required. Keep values as
 strings, including optional `EPP_PROVIDER_TIMEOUT_MS: "1500"`. Replace placeholders; provider API
 keys belong in the manifest-named Key Vault secrets, not this file. See the
-[complete variable table](../README.md#configure-environment-variables).
+[complete variable table](../TECHNICAL.md#configure-environment-variables).
 
 Core Tools loads `Values` into `os.environ`. Direct Python execution and pytest do not automatically
 read local settings. [read_config](src/config.py) returns an `AppConfig` object; the handler/engine