feat: add Coder Ping Workspace command (#749)

Add a `coder.pingWorkspace` command that runs `coder ping <workspace>`
locally and streams output to a custom PTY terminal. This helps users
diagnose connection problems by showing latency, P2P diagnostics, and
DERP info in real-time.

The command supports three invocation modes:
- Command Palette: shows a workspace picker (filtered to running)
- Sidebar context menu: under a new "Diagnostics" submenu
- When connected: pings the current workspace automatically

Other changes:
- Extract `resolveCliEnv` to deduplicate CLI bootstrap boilerplate
- Parameterize `pickWorkspace` with filter/title options and fix
  QuickPick disposal leak
- Encode workspace running status in tree item contextValue using a
  tag-based format (e.g. `coderWorkspaceSingleAgent+running`) so
  status-dependent menus use regex matching

Author: EhabY

package.json

@@ -259,6 +259,12 @@
 				"when": "!coder.authenticated && coder.loaded"
 			}
 		],
+		"submenus": [
+			{
+				"id": "coder.diagnostics",
+				"label": "Diagnostics"
+			}
+		],
 		"commands": [
 			{
 				"command": "coder.login",
@@ -363,6 +369,11 @@
 				"command": "coder.applyRecommendedSettings",
 				"title": "Apply Recommended SSH Settings",
 				"category": "Coder"
+			},
+			{
+				"command": "coder.pingWorkspace",
+				"title": "Ping Workspace",
+				"category": "Coder"
 			}
 		],
 		"menus": {
@@ -391,6 +402,10 @@
 					"command": "coder.navigateToWorkspaceSettings",
 					"when": "coder.workspace.connected"
 				},
+				{
+					"command": "coder.pingWorkspace",
+					"when": "coder.authenticated"
+				},
 				{
 					"command": "coder.workspace.update",
 					"when": "coder.workspace.updatable"
@@ -485,18 +500,28 @@
 			"view/item/context": [
 				{
 					"command": "coder.openFromSidebar",
-					"when": "coder.authenticated && viewItem == coderWorkspaceSingleAgent || coder.authenticated && viewItem == coderAgent",
+					"when": "coder.authenticated && viewItem =~ /^coderWorkspaceSingleAgent/ || coder.authenticated && viewItem =~ /^coderAgent/",
 					"group": "inline"
 				},
 				{
 					"command": "coder.navigateToWorkspace",
-					"when": "coder.authenticated && viewItem == coderWorkspaceSingleAgent || coder.authenticated && viewItem == coderWorkspaceMultipleAgents",
+					"when": "coder.authenticated && viewItem =~ /^coderWorkspaceSingleAgent/ || coder.authenticated && viewItem =~ /^coderWorkspaceMultipleAgents/",
 					"group": "inline"
 				},
 				{
 					"command": "coder.navigateToWorkspaceSettings",
-					"when": "coder.authenticated && viewItem == coderWorkspaceSingleAgent || coder.authenticated && viewItem == coderWorkspaceMultipleAgents",
+					"when": "coder.authenticated && viewItem =~ /^coderWorkspaceSingleAgent/ || coder.authenticated && viewItem =~ /^coderWorkspaceMultipleAgents/",
 					"group": "inline"
+				},
+				{
+					"submenu": "coder.diagnostics",
+					"when": "coder.authenticated && viewItem =~ /\\+running/",
+					"group": "navigation"
+				}
+			],
+			"coder.diagnostics": [
+				{
+					"command": "coder.pingWorkspace"
 				}
 			],
 			"statusBar/remoteIndicator": [