Fix spec/dummy Procfile.dev SERVER_BUNDLE_ONLY to match template convention (#2922)

## Summary
- Aligns `spec/dummy/Procfile.dev` to use `SERVER_BUNDLE_ONLY=yes`
instead of `=true`, matching the generator template and all other
Procfiles in the codebase
- Also fixes `CLIENT_BUNDLE_ONLY=true` → `=yes` in the RSC "how it
works" doc, which had the same inconsistency
- Both inconsistencies are purely cosmetic — webpack configs check
truthiness (`if (process.env.X)`), not exact string equality

## Context
- The `SERVER_BUNDLE_ONLY` inconsistency was introduced accidentally in
PR #1630 (June 2024) when the value was changed from `=yes` to `=true`
without review
- The `CLIENT_BUNDLE_ONLY` inconsistency in
`docs/pro/react-server-components/how-react-server-components-work.md`
was found during investigation — all other `CLIENT_BUNDLE_ONLY` usage
(`server_manager.rb`, specs, other docs) uses `=yes`

Closes #2409

## Test plan
- [x] CI passes (no functional change — both `"yes"` and `"true"` are
truthy in JS)
- [x] Verify `spec/dummy/Procfile.dev` now matches the template
convention
- [x] Verify RSC doc commands match the codebase convention

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Updated development/build configuration to adjust a server bundle
setting for consistent local tooling behavior.
* Updated documentation to reflect the revised build command and clarify
the local development workflow.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ihabadham

docs/pro/react-server-components/how-react-server-components-work.md

@@ -87,11 +87,11 @@ Let's examine the `react-client-manifest.json` file.
 First, you need to build the client bundle by running:
 
 ```bash
-CLIENT_BUNDLE_ONLY=true bin/shakapacker
+CLIENT_BUNDLE_ONLY=yes bin/shakapacker
 ```
 
 > [!NOTE]
-> When you run `bin/dev`, the client bundle may not be written to the disk, it's served from the webpack-dev-server. That's why you need to run `CLIENT_BUNDLE_ONLY=true bin/shakapacker` to ensure the client bundle is built and written to the disk.
+> When you run `bin/dev`, the client bundle may not be written to the disk, it's served from the webpack-dev-server. That's why you need to run `CLIENT_BUNDLE_ONLY=yes bin/shakapacker` to ensure the client bundle is built and written to the disk.
 
 Then, you can find the `react-client-manifest.json` file in the `public/webpack/development` or `public/webpack/production` directory, depending on the environment you are building for.
 

react_on_rails/spec/dummy/Procfile.dev

@@ -2,7 +2,7 @@
 # You can run these commands in separate shells
 rails: bundle exec rails s -p 3000
 dev-server: bin/shakapacker-dev-server
-server-bundle: SERVER_BUNDLE_ONLY=true bin/shakapacker-watch --watch
+server-bundle: SERVER_BUNDLE_ONLY=yes bin/shakapacker-watch --watch
 
 # Bundle ReScript .res files
 rescript: pnpm build:rescript:dev