docs: Apply documentation standards across all docs (#49177)

## Summary

Comprehensive remediation of 146 documentation files to align with Zed's
documentation conventions and brand voice guidelines.

## Changes

### YAML Frontmatter
- Added `title` and `description` frontmatter to all docs missing it

### Settings UI Pattern
- Updated 48+ files to show Settings Editor before JSON examples
- Pattern: `Configure X in Settings ({#kb zed::OpenSettings}), or add to
your settings file:`
- Added `([how to edit](./configuring-zed.md#settings-files))` links for
JSON-only settings

### Brand Voice Fixes
- Removed exclamation points (command-palette, key-bindings, repl,
privacy-and-security, etc.)
- Simplified em dash chains to parentheticals (environment,
troubleshooting, agent-panel, etc.)
- Fixed marketing language (yarn.md intro, development/linux.md)

### Terminology Alignment
- `settings UI` -> `Settings Editor`
- `sidebar` -> specific panel names (Project Panel, Collab Panel)
- `directory` -> `folder` in non-technical contexts
- `workspace` -> `project` in non-LSP contexts
- `Command Palette` -> `command palette` (lowercase)

### Callout Standardization
- Converted various callout formats to standard `> **Note:**` pattern

## Related

Depends on conventions established in #49176.

Release Notes:

- N/A

docs/src/languages/php.md

@@ -1,3 +1,8 @@
+---
+title: PHP
+description: "Configure PHP language support in Zed, including language servers, formatting, and debugging."
+---
+
 # PHP
 
 PHP support is available through the [PHP extension](https://github.com/zed-extensions/php).
@@ -39,7 +44,7 @@ The PHP extension uses [LSP language servers](https://microsoft.github.io/langua
 
 [Intelephense](https://intelephense.com/) is a [proprietary](https://github.com/bmewburn/vscode-intelephense/blob/master/LICENSE.txt#L29) language server for PHP operating under a freemium model. Certain features require purchase of a [premium license](https://intelephense.com/buy).
 
-To use Intelephense, add the following to your `settings.json`:
+Configure language servers in Settings ({#kb zed::OpenSettings}) under Languages > PHP, or add to your settings file:
 
 ```json [settings]
 {
@@ -71,7 +76,7 @@ Alternatively, you can pass the licence key or a path to a file containing the l
 
 [PHP Tools](https://www.devsense.com/) is a proprietary language server that offers free and premium features. You need to [purchase a license](https://www.devsense.com/en/purchase) to activate the premium features.
 
-To use PHP Tools, add the following to your `settings.json`:
+Configure language servers in Settings ({#kb zed::OpenSettings}) under Languages > PHP, or add to your settings file:
 
 ```json [settings]
 {
@@ -107,7 +112,7 @@ Check out the documentation of [PHP Tools for Zed](https://docs.devsense.com/oth
 
 ### Phpactor
 
-To use Phpactor instead of Intelephense or any other tools, add the following to your `settings.json`:
+Configure language servers in Settings ({#kb zed::OpenSettings}) under Languages > PHP, or add to your settings file:
 
 ```json [settings]
 {