Fix action.yml for GitHub Marketplace publish validation (#629)

GitHub Marketplace rejected the action on publish:
- name `mdsmith` is not unique (must not match an existing action, user, or
  organization name)
- description exceeded the 125-character limit

Rename the action to `mdsmith Markdown linter` and shorten the description
to 98 chars. Point the channel doc's Marketplace URL at the new slug
(mdsmith-markdown-linter).

https://claude.ai/code/session_01TKgJTS4UcFPqtdwkxYzTUC

Co-authored-by: Claude <noreply@anthropic.com>

Author: jeduden

action.yml

@@ -1,8 +1,7 @@
-name: mdsmith
+name: mdsmith Markdown linter
 description: >-
-  Install the mdsmith Markdown linter from a checksum-verified GitHub release
-  binary for the runner's OS and architecture, put it on PATH, and optionally
-  run a mdsmith command.
+  Install the mdsmith Markdown linter from a checksum-verified
+  release binary and optionally run it.
 author: jeduden
 branding:
   icon: check-square

docs/development/release-channels/github-actions.md

@@ -14,13 +14,13 @@ platforms: [linux, macos, windows]
 registry: github.com/marketplace
 credential: GITHUB_TOKEN
 job: release
-channelurl: https://github.com/marketplace/actions/mdsmith
+channelurl: https://github.com/marketplace/actions/mdsmith-markdown-linter
 weight: 15
 unlisted: true
 ---
 # GitHub Actions
 
-Release page: <https://github.com/marketplace/actions/mdsmith>
+Release page: <https://github.com/marketplace/actions/mdsmith-markdown-linter>
 
 The repository root carries an `action.yml`, so a workflow
 step runs mdsmith with: