fix: second pass - navigation flow, backward links, and content issues

[mtahle]

Navigation & flow fixes:

• Add forward CTA buttons to linux/index.md, containers/index.md, automation/index.md so section indexes lead into their first page
• Fix linux/introduction.md next-steps order to match nav sequence (web-hosting → advanced-hosting → troubleshooting-tools, was reversed)
• Remove backward links from concepts/domains-dns.md (web-development), concepts/protocols.md (domains-dns, web-development), concepts/ssl.md (domains-dns, containers/security jump)
• Reorder concepts/web-development.md next steps to match nav order (domains-dns → protocols → ssl → hosting, was hosting first)
• Reorder concepts/internet-basics.md next steps to match nav order
• Fix linux/web-hosting.md: remove forward-skipping links to monitoring; chain to advanced-hosting → troubleshooting-tools instead
• Fix linux/advanced-hosting.md: replace unlinked "Container Orchestration" text with link to containers/index.md; remove monitoring forward-skip
• Fix linux/troubleshooting-tools.md: remove backward links to earlier linux pages; point forward to containers/index.md
• Fix containers/kubernetes-production.md: replace three plain-text next-step items with links to automation/index.md and advanced/index.md
• Fix containers/security.md: replace unlinked "Service Mesh" text with link to advanced/index.md
• Fix automation/container-cicd.md: replace two unlinked next-step items with links to monitoring and advanced/index.md

Content fixes:

• Fix protocols.md: replace misplaced OpenSSL code block in "Special IP Addresses" section with correct special address reference table
• Fix monitoring/index.md: remove phantom mermaid nodes (Advanced Monitoring, Alerting & Response, Log Management, Observability) that reference non-existent pages
• Fix introduction/index.md: remove "Metrics, Feedback (future section)" entry from Reading Path since the page does not exist
• Fix introduction/practices.md: remove "(placeholder)" and "(future advanced topic placeholder)" inline labels from GitOps and Policy as Code items
• Fix concepts/index.md: correct page title from "DevOps Fundamentals" to "Network & Web Fundamentals" to match nav section label
• Fix docs/index.md: add Foundations as step 1 in the Learning Path; it was absent despite being the first nav section