fix: fix API docstrings for proper MDX parsing (#3526)

# What does this PR do?

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_[Stack 1/10] Docusaurus documentation migration_

Updates the file upload API documentation to use proper OpenAPI format for integer parameters. Replaces `<int>` with `{integer}` in the description of the `expires_after[seconds]` parameter across the HTML spec, YAML spec, and Python implementation.

## Test Plan

- docs/openapi_generator/run_openapi_generator.sh

<!-- Describe the tests you ran to verify your changes with result summaries. *Provide clear instructions so the plan can be easily re-executed.* -->

docs/_static/llama-stack-spec.html

@@ -4451,7 +4451,7 @@
                 "tags": [
                     "Files"
                 ],
-                "description": "Upload a file that can be used across various endpoints.\nThe file upload should be a multipart form request with:\n- file: The File object (not file name) to be uploaded.\n- purpose: The intended purpose of the uploaded file.\n- expires_after: Optional form values describing expiration for the file. Expected expires_after[anchor] = \"created_at\", expires_after[seconds] = <int>. Seconds must be between 3600 and 2592000 (1 hour to 30 days).",
+                "description": "Upload a file that can be used across various endpoints.\nThe file upload should be a multipart form request with:\n- file: The File object (not file name) to be uploaded.\n- purpose: The intended purpose of the uploaded file.\n- expires_after: Optional form values describing expiration for the file. Expected expires_after[anchor] = \"created_at\", expires_after[seconds] = {integer}. Seconds must be between 3600 and 2592000 (1 hour to 30 days).",
                 "parameters": [],
                 "requestBody": {
                     "content": {

docs/_static/llama-stack-spec.yaml

@@ -3164,7 +3164,7 @@ paths:
         - purpose: The intended purpose of the uploaded file.
 
         - expires_after: Optional form values describing expiration for the file.
-        Expected expires_after[anchor] = "created_at", expires_after[seconds] = <int>.
+        Expected expires_after[anchor] = "created_at", expires_after[seconds] = {integer}.
         Seconds must be between 3600 and 2592000 (1 hour to 30 days).
       parameters: []
       requestBody:

llama_stack/apis/files/files.py

@@ -119,7 +119,7 @@ class Files(Protocol):
         The file upload should be a multipart form request with:
         - file: The File object (not file name) to be uploaded.
         - purpose: The intended purpose of the uploaded file.
-        - expires_after: Optional form values describing expiration for the file. Expected expires_after[anchor] = "created_at", expires_after[seconds] = <int>. Seconds must be between 3600 and 2592000 (1 hour to 30 days).
+        - expires_after: Optional form values describing expiration for the file. Expected expires_after[anchor] = "created_at", expires_after[seconds] = {integer}. Seconds must be between 3600 and 2592000 (1 hour to 30 days).
 
         :param file: The uploaded file object containing content and metadata (filename, content_type, etc.).
         :param purpose: The intended purpose of the uploaded file (e.g., "assistants", "fine-tune").