fix(opencode): pass VERSION to bash instead of curl in install pipe (#815)

## Summary

- Fix version pinning bug in the OpenCode install script
(`registry/coder-labs/modules/opencode/scripts/install.sh`, line 42)

**Bug:** The install command was:
```bash
VERSION=$ARG_OPENCODE_VERSION curl -fsSL https://opencode.ai/install | bash
```

`VERSION` was set as an environment variable prefix to `curl` (the left
side of the pipe), so the `bash` process on the right side of the pipe
never received it. In a shell pipeline, each command runs in its own
subprocess, so env var prefixes only apply to the immediately following
command. This caused the installer script to always install the latest
version instead of the pinned version specified by the user.

**Fix:** Move `VERSION` to prefix `bash` instead of `curl`:
```bash
curl -fsSL https://opencode.ai/install | VERSION=$ARG_OPENCODE_VERSION bash
```

Now the `VERSION` variable is correctly available to the install script
executed by `bash`.

## Test plan

- [x] Set `opencode_version` to a specific version (e.g., `0.1.0`) and
verify that version is installed instead of latest
- [x] Set `opencode_version` to `latest` and verify the latest version
is still installed (this code path is unchanged)
- [x] Verify `opencode --version` output matches the requested version
after install

---------

Co-authored-by: 35C4n0r <70096901+35C4n0r@users.noreply.github.com>

registry/coder-labs/modules/opencode/README.md

@@ -13,7 +13,7 @@ Run [OpenCode](https://opencode.ai) AI coding assistant in your workspace for in
 ```tf
 module "opencode" {
   source   = "registry.coder.com/coder-labs/opencode/coder"
-  version  = "0.1.1"
+  version  = "0.1.2"
   agent_id = coder_agent.main.id
   workdir  = "/home/coder/project"
 }
@@ -34,7 +34,7 @@ resource "coder_ai_task" "task" {
 
 module "opencode" {
   source   = "registry.coder.com/coder-labs/opencode/coder"
-  version  = "0.1.1"
+  version  = "0.1.2"
   agent_id = coder_agent.main.id
   workdir  = "/home/coder/project"
 
@@ -89,7 +89,7 @@ Run OpenCode as a command-line tool without web interface or task reporting:
 ```tf
 module "opencode" {
   source       = "registry.coder.com/coder-labs/opencode/coder"
-  version      = "0.1.1"
+  version      = "0.1.2"
   agent_id     = coder_agent.main.id
   workdir      = "/home/coder"
   report_tasks = false

registry/coder-labs/modules/opencode/scripts/install.sh

@@ -39,7 +39,7 @@ install_opencode() {
       if [ "$ARG_OPENCODE_VERSION" = "latest" ]; then
         curl -fsSL https://opencode.ai/install | bash
       else
-        VERSION=$ARG_OPENCODE_VERSION curl -fsSL https://opencode.ai/install | bash
+        curl -fsSL https://opencode.ai/install | VERSION="${ARG_OPENCODE_VERSION}" bash
       fi
       export PATH=/home/coder/.opencode/bin:$PATH
       printf "Opencode location: %s\n" "$(which opencode)"