Add Episode 7 empty blog baseline

[KalebCole]

Why

Episode 7 needs a frozen recording starting state where Jamie Rivera's blog functionality already exists but has no published posts. The episode will create and publish the first post on camera rather than teach the blog feature itself.

What

• Extends the Jamie Rivera Episode 2 portfolio merged in commit aab5fdf72c21520c12a435528cb2d09c28f418f1
• Preserves its responsive layout, dark mode, accessibility, updated content, and resume preview/download
• Adds a homepage Blog section with a persistent link to the style-matched full blog page
• Adds blog/posts-src/ Markdown sources, blog/posts/ generated HTML, posts.json listing metadata, and a standard-library static generator

This PR is the frozen Episode 7 recording starting state and contains no published post.

Validation

• Served episode-07/portfolio/ over local HTTP and verified all local homepage/blog references return successfully
• Verified homepage Blog scrolling, full-blog navigation, Blog-to-Home navigation, dark mode, and mobile menu behavior
• Verified relative paths work from the portfolio root and generated post depth
• Confirmed zero post cards, metadata entries, source drafts, and published HTML files
• Exercised the Markdown parser/renderer with representative headings, emphasis, lists, and metadata
• Completed a focused Rubber Duck review for paths, behavior, accessibility, and prompt-contract alignment