Post images as page bundle resources

Every image a post uses lives in the post’s branch bundle, beside index.md, so Hugo exposes it as a page resource resolvable by bare filename.

Every image file a post uses sits in the root of that post’s bundle: no images/ sub-folder remains under content/, and no post image lives in static/img/ (only site chrome: favicon.png, apple-icon.png).
Every image path written in a post body resolves to a resource of that post. The two .png references in content/post/cryengine/matrices-vectors-quaternions-and-cryengine-3/index.md pointed at files that were never in the bundle; they now show the glyphs they depicted, φ, θ, ψ and ℍ.
Image resources keep bare filenames, so the imgB-<md5>-LQIP class the render hooks emit matches the class generated by be-best/layouts/_partials/images/image-process.html. All 7 image paths in post bodies are bare filenames, and each has a matching rule in the <style> block of the page that uses it.

Acceptance Criteria

find content -type d -name images prints nothing.
grep -rl '/img/' content/post prints nothing.
hugo --quiet succeeds and grep -rl 'Image unavailable' public/post/ prints nothing.
For content/post/cryengine/creating-interesting-terrain/world-machine.webp, the imgB-<md5> class in the article HTML matches a rule in the generated <style> block of that page.
The four content/post/general/building-a-joystick/*.jpeg resources, which no post body references, are named as carousel slides by p2-ft-post-image-carousel.

Responsive carousel rendering of the enumerated images: p2-ft-post-image-carousel.
Scaling, format conversion and compression: p2-us-image-processing.
Featured image srcset sizing in cards: p2-us-featured-images.