Make value_hint optional to allow constant positional arguments (#172)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->

This is one attempt to resolve
https://github.com/modelcontextprotocol/registry/issues/169.

Instead of adding a new "constant" argument type, I expanded the
existing positional one and just dropped the `value_hint` requirement. I
am not sure if this has VS Code impact @sandy081, @connor4312.

Also, removed unneeded release_date values from the samples.

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

I tested the current server.json samples in the repo against the new
(less strict) schema. Of course they passed (aside from an unrelated bug
in my previous NuGet sample 🤦).

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

docs/server-json/examples.md

@@ -12,8 +12,7 @@
     "id": "abc123de-f456-7890-ghij-klmnopqrstuv"
   },
   "version_detail": {
-    "version": "1.0.2",
+    "version": "1.0.2"
-    "release_date": "2023-06-15T10:30:00Z"
   },
   "packages": [
     {
@@ -33,6 +32,39 @@
 }
 ```
 
+## Constant (fixed) arguments needed to start the MCP server
+
+Suppose your MCP server application requires a `mcp start` CLI arguments to start in MCP server mode. Express these as positional arguments like this:
+
+```json
+{
+  "name": "Knapcode.SampleMcpServer",
+  "description": "Sample NuGet MCP server for a random number and random weather",
+  "version_detail": {
+    "version": "0.4.0-beta"
+  },
+  "packages": [
+    {
+      "registry_name": "nuget",
+      "name": "Knapcode.SampleMcpServer",
+      "version": "0.4.0-beta",
+      "package_arguments": [
+        {
+          "type": "positional",
+          "value": "mcp"
+        },
+        {
+          "type": "positional",
+          "value": "start"
+        }
+      ]
+    }
+  ]
+}
+```
+
+This will essentially instruct the MCP client to execute `dnx Knapcode.SampleMcpServer@0.4.0-beta -- mcp start` instead of the default `dnx Knapcode.SampleMcpServer@0.4.0-beta` (when no `package_arguments` are provided).
+
 ## Filesystem Server with Multiple Packages
 
 ```json
@@ -45,8 +77,7 @@
     "id": "b94b5f7e-c7c6-d760-2c78-a5e9b8a5b8c9"
   },
   "version_detail": {
-    "version": "1.0.2",
+    "version": "1.0.2"
-    "release_date": "2023-06-15T10:30:00Z"
   },
   "packages": [
     {
@@ -128,8 +159,7 @@
     "id": "xyz789ab-cdef-0123-4567-890ghijklmno"
   },
   "version_detail": {
-    "version": "2.0.0",
+    "version": "2.0.0"
-    "release_date": "2024-01-20T14:30:00Z"
   },
   "remotes": [
     {
@@ -152,8 +182,7 @@
     "id": "def456gh-ijkl-7890-mnop-qrstuvwxyz12"
   },
   "version_detail": {
-    "version": "0.5.0",
+    "version": "0.5.0"
-    "release_date": "2024-02-10T09:15:00Z"
   },
   "packages": [
     {
@@ -189,11 +218,11 @@ The `dnx` tool ships with the .NET 10 SDK, starting with Preview 6.
   "description": "Sample NuGet MCP server for a random number and random weather",
   "repository": {
     "url": "https://github.com/joelverhagen/Knapcode.SampleMcpServer",
-    "source": "github"
+    "source": "github",
+    "id": "def456gh-ijkl-7890-mnop-qrstuvwxyz13"
   },
   "version_detail": {
-    "version": "0.3.0",
+    "version": "0.3.0-beta"
-    "release_date": "2025-07-02T18:54:28.00Z"
   },
   "packages": [
     {
@@ -226,8 +255,7 @@ The `dnx` tool ships with the .NET 10 SDK, starting with Preview 6.
     "id": "ghi789jk-lmno-1234-pqrs-tuvwxyz56789"
   },
   "version_detail": {
-    "version": "3.1.0",
+    "version": "3.1.0"
-    "release_date": "2024-03-05T16:45:00Z"
   },
   "packages": [
     {
@@ -313,8 +341,7 @@ The `dnx` tool ships with the .NET 10 SDK, starting with Preview 6.
     "id": "klm012no-pqrs-3456-tuvw-xyz789abcdef"
   },
   "version_detail": {
-    "version": "1.5.0",
+    "version": "1.5.0"
-    "release_date": "2024-04-01T12:00:00Z"
   },
   "packages": [
     {

docs/server-json/schema.json

@@ -196,8 +196,7 @@
         {
           "type": "object",
           "required": [
-            "type",
+            "type"
-            "value_hint"
           ],
           "properties": {
             "type": {
@@ -217,7 +216,19 @@
               "description": "Whether the argument can be repeated multiple times in the command line.",
               "default": false
             }
-          }
+          },
+          "anyOf": [
+            {
+              "required": [
+                "value_hint"
+              ]
+            },
+            {
+              "required": [
+                "value"
+              ]
+            }
+          ]
         }
       ]
     },

docs/server-registry-api/openapi.yaml

@@ -247,7 +247,6 @@ components:
         - type: object
           required:
             - type
-            - value_hint
           properties:
             type:
               type: string
@@ -261,6 +260,11 @@ components:
               type: boolean
               description: Whether the argument can be repeated multiple times in the command line.
               default: false
+          anyOf:
+            - required:
+                - value
+            - required:
+                - value_hint
 
     NamedArgument:
       description: A command-line `--flag={value}`.