docs: focus the site on the language, one door and seven pages

[josemontesdeoca]

The docs site now covers the language and nothing else, as one door and seven pages: what OpenProse is, setup via the skill, declaring outcomes, contracts, ProseScript, the typed image, and the harness seam.

Structure

• The harness sections (/reactor, /sdk, /cli, /reactor-devtools) are removed. That reference lives with the packages in the openprose/prose repo, and the old routes redirect there. The redirects are temporary on purpose: the routes may host docs again when the harness documentation is reworked.
• The section folder is gone too: with one topic left it forced every visitor through two overview pages with the same job. Pages live at the root in learning order, and every old /openprose/* link redirects to its new home.

Reading path

• Setup teaches the skill path: install, author a complete first contract, run that exact file, and where to file an issue when something breaks. Agent-filed issues are first-class here, same as the main repo.
• The language pages keep the seam honest: fingerprints, memoization, and receipts are one host's runtime, not language features. Reactor is named once, as one such host, pointing at the repo for the harness reference.

Rendering

• The contracts page's program panels no longer inherit the inline-code chip styling that painted a box behind every line.
• Markdown fences soft-wrap on narrow viewports so their sentences stay readable; alignment-sensitive fences keep their horizontal scroll.
• Prose no longer renders literal double hyphens where a dash was meant, and the one four-column table folds its overflow column into the paragraph below it.
• The theme toggle is removed: the site is light-only by design and the control did nothing.

Checks: typecheck, tests, lint, spell, the em-dash gate, and the internal link checker all pass.