Add Double Letter Slot Tour rarity and cached detection

[tphummel]

Motivation

• Add a new derived rarity for puzzles that tour two letters (both letters appear in slots 1–5 across all guesses) and expose it in the reports and per-puzzle achievements.
• Reuse the existing single-letter slot coverage work so double detection is efficient and cache-friendly.

Description

• Added a new report page content/double-letter-slot-tour.md that lists puzzles with double-letter slot tours and clarifies the definition as coverage "across all guesses".
• Extended layouts/partials/letter-counts.html to compute a _doubles list by combining already-detected _singles, avoiding a second scan of guess data.
• Added a new partial layouts/partials/double-letter-guesses.html that returns puzzles containing one or more double-letter tours.
• Wired the new rarity into the homepage (layouts/index.html), per-puzzle achievements (layouts/w/single.html) with badge 🔂, and p8s metrics output (layouts/index.p8s.txt), and clarified the letter-slot-tour page text.
• Use partialCached for aggregating both single and double lists so results are cached and lookups are efficient.

Testing

• Ran the unit test node static/tools/enhance/enrich-emoji.test.js and it completed successfully.
• Attempted a Hugo build; asdf exec hugo failed in this environment because asdf is unavailable, and hugo --templateMetrics was started but did not complete within the execution timeframe.
• Verified templates and partials were updated and the new pages/partials were added (content/double-letter-slot-tour.md, layouts/partials/double-letter-guesses.html, and layouts/partials/letter-counts.html).

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Codex Task

[cloudflare-workers-and-pages]

Deploying wordle with    Cloudflare Pages

Latest commit:	ce16d86
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Branch Preview URL:	https://ai-add-double-letter-slot-to.wordle-static.pages.dev

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