Fix broken links from link-checker report

[yashrajshuklaaa]

Fix broken links from link-checker report #457

Fixes 25 broken or outdated links across 17 files, flagged by the automated link checker in report #457.
Changes include:

• Updated redirected/moved doc URLs (MCP protocol docs, Google ADK docs to adk.dev, Slack API docs, AWS Bedrock, Google Cloud auth, Claude docs)
• Fixed A2A protocol spec links (a2a.guide to a2a-protocol.org)
• Corrected GitHub org for FastMCP Python (jlowin to PrefectHQ)
• Removed unnecessary .git suffix and www. prefixes from a few links
• Wrapped a bare example URL in backticks in the API reference table

Not addressed (out of scope, needs follow-up):

• servereverything.dev/mcp: unclear if the 406 is a false positive or a genuinely broken URL
• 4 kubernetes.io/git.k8s.io anchor warnings: outside this repo's control

All new links verified to resolve (200 OK). No changes to Markdown link syntax or file structure elsewhere in the affected pages.

[Rachael-Graham]

Hi @yashrajshuklaaa - We ran a script yesterday to fully port over the docs site to be sourced from the docs-site/content/kagent *.md files which run with the repo's new theme, and removed the outdated *.mdx files by removing the src/app/docs directory. You can check whether these same broken link fixes exist in the equivalent markdown files (I am running the link check action here https://github.com/kagent-dev/website/actions/runs/32382407309 to see what it picks up from the new markdown files), or can close the PR