docs(hcp-vault-secrets): deprecation notice (#199)

## Description

<!-- Briefly describe what this PR does and why -->
add deprecation notice and migration guidance to README

## Type of Change

- [ ] New module
- [ ] Bug fix
- [ ] Feature/enhancement
- [ ] Documentation
- [X] Other

## Module Information

<!-- Delete this section if not applicable -->

**Path:** `registry/coder/modules/hcp-vault-secrets`  
**New version:** `v1.0.8`  
**Breaking change:** [ ] Yes [X] No

## Testing & Validation

- [X] Tests pass (`bun test`)
- [X] Code formatted (`bun run fmt`)
- [NA] Changes tested locally

## Related Issues

<!-- Link related issues or write "None" if not applicable -->
None

Author: DevelopmentCats

registry/coder/modules/hcp-vault-secrets/README.md

@@ -10,12 +10,25 @@ tags: [integration, vault, hashicorp, hvs]
 
 # HCP Vault Secrets
 
+> [!WARNING]
+> **⚠️ DEPRECATED: HCP Vault Secrets is being sunset**
+>
+> HashiCorp has announced that HCP Vault Secrets will no longer be available for purchase by new customers after **June 30th, 2025**. This module will stop working when HCP Vault Secrets is fully discontinued.
+>
+> **Use these Coder registry modules instead:**
+>
+> - **[vault-token](https://registry.coder.com/modules/vault-token)** - Connect to Vault using access tokens
+> - **[vault-jwt](https://registry.coder.com/modules/vault-jwt)** - Connect to Vault using JWT/OIDC authentication
+> - **[vault-github](https://registry.coder.com/modules/vault-github)** - Connect to Vault using GitHub authentication
+>
+> These modules work with both self-hosted Vault and HCP Vault Dedicated. For migration help, see the [official HashiCorp announcement](https://developer.hashicorp.com/hcp/docs/vault-secrets/end-of-sale-announcement).
+
 This module lets you fetch all or selective secrets from a [HCP Vault Secrets](https://developer.hashicorp.com/hcp/docs/vault-secrets) app into your [Coder](https://coder.com) workspaces. It makes use of the [`hcp_vault_secrets_app`](https://registry.terraform.io/providers/hashicorp/hcp/latest/docs/data-sources/vault_secrets_app) data source from the [HCP provider](https://registry.terraform.io/providers/hashicorp/hcp/latest).
 
 ```tf
 module "vault" {
   source     = "registry.coder.com/coder/hcp-vault-secrets/coder"
-  version    = "1.0.7"
+  version    = "1.0.8"
   agent_id   = coder_agent.example.id
   app_name   = "demo-app"
   project_id = "aaa-bbb-ccc"
@@ -41,7 +54,7 @@ To fetch all secrets from the HCP Vault Secrets app, skip the `secrets` input.
 ```tf
 module "vault" {
   source     = "registry.coder.com/coder/hcp-vault-secrets/coder"
-  version    = "1.0.7"
+  version    = "1.0.8"
   agent_id   = coder_agent.example.id
   app_name   = "demo-app"
   project_id = "aaa-bbb-ccc"
@@ -55,7 +68,7 @@ To fetch selective secrets from the HCP Vault Secrets app, set the `secrets` inp
 ```tf
 module "vault" {
   source     = "registry.coder.com/coder/hcp-vault-secrets/coder"
-  version    = "1.0.7"
+  version    = "1.0.8"
   agent_id   = coder_agent.example.id
   app_name   = "demo-app"
   project_id = "aaa-bbb-ccc"
@@ -70,7 +83,7 @@ Set `client_id` and `client_secret` as module inputs.
 ```tf
 module "vault" {
   source        = "registry.coder.com/coder/hcp-vault-secrets/coder"
-  version       = "1.0.7"
+  version       = "1.0.8"
   agent_id      = coder_agent.example.id
   app_name      = "demo-app"
   project_id    = "aaa-bbb-ccc"