Fix empty module list and blank README pages (#765)

[h3nnes]

Symptoms: the module list came up empty and detail pages showed nothing. There were two independent causes.

1. DNS. With the "doh" setting on, CloudflareDNS resolved every host only through cloudflare-dns.com (bootstrapped on 1.1.1.1) with no fallback. Where Cloudflare is blocked, every lookup fails immediately, so the list, per-module detail and GitHub all fail at once and the app is unusable until DoH is turned off by hand. DoH is now best-effort: on failure it falls back to the system resolver, remembers the failure for the session, and uses a short DoH timeout so the first fallback is quick. This is the fix for the reported empty list.

2. Endpoints. The old mirror chain no longer serves the list: modules.lsposed.org returns 403 for modules.json, modules-blogcdn returns 418, and modules-cloudflare has no DNS record. Only backup.modules.lsposed.org still serves modules.json; per-module detail (module/.json) is served by both backup and modules.lsposed.org. The single mirror list is split accordingly (list -> backup only; detail -> backup then modules.lsposed.org) and the dead mirrors dropped.

Alongside those:

• Treat non-2xx and empty/blank/invalid responses as load failures rather than silent successes, and restore the loaded state after a failed refresh so the UI never hangs refreshing. Keep cached data when a remote refresh fails.
• README: the list payload no longer reliably carries README/releases, so detail is fetched per module on demand. When detail lacks a README, or all detail mirrors are down, fall back to the module's GitHub repo (github.com/Xposed-Modules-Repo/) for the rendered README. The README tab shows a loading state while detail downloads instead of the empty placeholder, and keeps the already-loaded richer module rather than flickering back to the leaner list summary on a repo refresh.
• Rendering: GitHub now emits the heading permalink anchor as a sibling after the heading, so markdown.css's old heading-descendant hide rule missed it and the floated link icon leaked into the left gutter; hide .anchor outright.
• "Open in browser" stays on modules.lsposed.org, whose per-module web page (unlike the JSON API host) returns HTML and has no .json suffix.
• Added logging (tag LSPosedManager, captured by the daemon verbose log) across list and detail loading so future empty-list/empty-detail reports are diagnosable.

Endpoint reference for maintainers:
backup.modules.lsposed.org modules.json 200, module/.json 200
modules.lsposed.org modules.json 403, module/.json 200, /module/ HTML 200
modules-blogcdn 418
modules-cloudflare no DNS record
Each module mirrors a GitHub repo at github.com/Xposed-Modules-Repo/
(README + releases), the ultimate source behind the GitHub fallbacks.

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