feat(home): deep-link and persist the A–Z article index letter in the URL

[dhgoal]

Summary

The home page's A–Z article index is a client-side letter filter, but the selected letter lives only in client state. This adds URL-hash deep-linking so the index behaves like the rest of the site's shareable surfaces — the same URL-state treatment the search facets got in #1955.

• Clicking a letter writes #<letter> to the URL via history.replaceState (no scroll jump, kept out of back-button history).
• An incoming #<letter> is honoured on first load and on hashchange (back/forward).
• The hash is validated to a single A–Z that actually has an article group, so a stray hash (e.g. the #content skip-link target) or a letter with no articles is ignored and the current selection is left untouched.

Scope is the home page's existing inline script only — no markup, styling, or layout changes.

Why This Should Ship

Issue #521 asks for stronger article discovery on the landing page. Today taopedia.org/#M just shows the default first letter — a shared or reloaded index link silently loses its place. After this, a reader (or a link) can jump straight to a letter and the choice survives reload and sharing. It reuses the exact URL-state pattern the maintainer already accepted for search facets (#1955). Refs #521.

Review Notes

• One file of behaviour (src/pages/index.astro inline script) + a test; package.json wires the test script.
• Test: npm run test:home-index-deeplink — scripts/check-home-index-deeplink.js pins the URL-state contract in source and executes the shipped inline script against a DOM stub, verifying deep-link on load, click→#letter persistence, hashchange resync, and that stray/foreign hashes are ignored.
• Progressive enhancement unchanged: with no hash (or JS off) the server-rendered default letter is shown exactly as before.

Before — visiting /#M ignores the hash (index stuck on the default letter)

After — visiting /#M deep-links straight to the M articles

Evidence is a faithful local render of the article-index section — the component's own CSS and the actual shipped inline script, loaded headless at …#M. The live change is also visible on the Netlify deploy preview.

Target Branch

• This PR targets test
• This PR targets main only because it promotes test to production

Security Checklist

• No secrets, tokens, build hooks, wallet seeds, or private endpoints are included
• No unnecessary workflow, dependency, or deployment changes

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Requested label: ui-ux

[taopedia-site-maintainer]

Verdict: Close

PR #1973: feat(home): deep-link and persist the A–Z article index letter in the URL

This PR changes toggle-driven on-screen behavior. Code analysis confirms the visible effect only appears during the interaction, so static before/after screenshots cannot demonstrate it (an identical-looking pair is not valid evidence). A short screen recording or GIF is required.

Visual PRs need evidence in the PR description so the maintainer can review the change quickly and reliably. A deploy preview link alone is not enough.

Required evidence for resubmission:

• Page URL.
• Viewport width, especially for responsive changes.
• Action taken (the toggle that reveals the change).
• Expected before behavior.
• Expected after behavior.
• A short video/GIF that shows the change happening during the interaction. Static screenshots alone are not accepted for this PR.

Changed files:

• package.json
• scripts/check-home-index-deeplink.js
• src/pages/index.astro

CI: Checks still pending: build

Please open a new focused PR with the required evidence attached.

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Automated review by Taopedia Site Maintainer.