fix(ci): copy CHANGELOG.md into the wasm docker stage — deploys broken since v0.47.0

whats_new_plugin embeds the changelog at compile time
(include_str!("../../CHANGELOG.md"), shipped 2026-07-13), but the
Dockerfile's wasm-builder stage copies an explicit file list that
never included CHANGELOG.md — every docker-build since (10 runs,
v0.48.x and v0.49.0 content) failed in build_wasm.sh while web-e2e
(full checkout) stayed green, so the web has been serving the
July 14 image.

Also add CHANGELOG.md to the workflow's trigger paths so changelog
cuts redeploy the web and the What's-new card stays fresh.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/docker-build.yml

@@ -15,6 +15,9 @@ on:
       - 'Cargo.toml'
       - 'Cargo.lock'
       - 'build_wasm.sh'
+      # The engine embeds CHANGELOG.md (What's-new card) — changelog cuts
+      # must redeploy the web so the card content stays fresh.
+      - 'CHANGELOG.md'
       - 'solitaire_server/Dockerfile'
       - '.gitea/workflows/docker-build.yml'