feat(web): port PoW challenge page from vanilla JS to Preact

Replace the imperative DOM manipulation in web/js/main.ts with a
declarative Preact component (web/js/main.tsx). The project already
uses Preact for the timed-delay challenge (lib/challenge/preact/),
so this aligns the PoW challenge with the existing codebase direction.

Convert web/js/main.ts to a Preact TSX component. The worker
orchestration layer (web/js/algorithms/fast.ts) stays untouched --
it is already cleanly separated and works via a Promise API.

web/js/main.ts -> web/js/main.tsx:
  - Phase-based state machine (loading -> computing -> reading/error)
    replaces scattered imperative DOM updates.
  - Worker lifecycle managed in useEffect; progress callback drives
    state setters for speed and progress percentage.
  - Speed updates remain throttled to 1 second intervals.
  - i18n functions (initTranslations, t(), loadTranslations) kept as
    module-level state -- no need for React context in a single-
    component app.
  - The <details> section stays in the templ file as server-rendered
    HTML; the Preact component tracks its toggle state via useRef.
  - Uses esbuild automatic JSX transform (--jsx=automatic
    --jsx-import-source=preact) instead of classic pragmas.

web/build.sh:
  - Add js/**/*.tsx to the glob so esbuild bundles TSX files.
  - Pass --jsx=automatic --jsx-import-source=preact for .tsx files.

web/tsconfig.json (new):
  - IDE-only config (noEmit) so TypeScript understands Preact JSX
    types for editor diagnostics and autocompletion.

lib/challenge/proofofwork/proofofwork.templ:
  - Replace individual DOM elements (img#image, p#status,
    div#progress) with a <div id="app"> Preact mount point
    containing server-rendered fallback (pensive image + loading
    text).
  - Keep <details>, <noscript>, and <div id="testarea"> outside the
    Preact tree as server-rendered content.

lib/anubis.go:
  - Add challenge method to the "new challenge issued" log line.

docs/docs/CHANGELOG.md:
  - Add entry for the Preact rewrite.

  - web/js/algorithms/fast.ts -- untouched
  - web/js/algorithms/index.ts -- untouched
  - web/js/worker/sha256-*.ts -- untouched
  - Server-side Go code (proofofwork.go) -- untouched
  - JSON script data embedding -- untouched
  - Redirect URL construction -- same logic, same parameters
  - Progress bar CSS in web/index.templ -- untouched

Signed-off-by: Xe Iaso <me@xeiaso.net>
Assisted-by: Claude Opus 4.6 via Claude Code
Signed-off-by: Xe Iaso <me@xeiaso.net>

web/build.sh

@@ -41,15 +41,22 @@ cp ../lib/localization/locales/*.json static/locales/
 
 shopt -s nullglob globstar
 
-for file in js/**/*.ts js/**/*.mjs; do
+for file in js/**/*.ts js/**/*.tsx js/**/*.mjs; do
   out="static/${file}"
-  if [[ "$file" == *.ts ]]; then
+  if [[ "$file" == *.tsx ]]; then
+    out="static/${file%.tsx}.mjs"
+  elif [[ "$file" == *.ts ]]; then
     out="static/${file%.ts}.mjs"
   fi
 
   mkdir -p "$(dirname "$out")"
 
-  esbuild "$file" --sourcemap --bundle --minify --outfile="$out" --banner:js="$LICENSE"
+  JSX_FLAGS=""
+  if [[ "$file" == *.tsx ]]; then
+    JSX_FLAGS="--jsx=automatic --jsx-import-source=preact"
+  fi
+
+  esbuild "$file" --sourcemap --bundle --minify --outfile="$out" $JSX_FLAGS --banner:js="$LICENSE"
   gzip -f -k -n "$out"
   zstd -f -k --ultra -22 "$out"
   brotli -fZk "$out"