feat: add Python and Java regex engines

public/engines/README.md

@@ -1,9 +1,13 @@
 # Engine assets
 
 Regex Tools executes ECMAScript through the browser's native `RegExp` engine.
-It also ships the declared, self-hosted PCRE2 10.47 WebAssembly pack in
-`pcre2/`.
+It also ships three declared, self-hosted runtime packs:
 
-The PCRE2 pack is built from pinned, documented open-source code and
-toolchain revisions. `engine-metadata.json`, `SHA256SUMS` and `LICENSE.txt`
-travel with the runtime files and are verified by the release gate.
+- `pcre2/`: official PCRE2 10.47, 8-bit WebAssembly;
+- `python/`: Pyodide 314.0.3 with CPython 3.14.2 `re`; and
+- `java/`: TeaVM 0.15.0's `java.util.regex` class library compiled to an
+  ES2015 module. This module is not OpenJDK.
+
+The packs come from pinned, documented open-source inputs. Runtime files travel
+with deterministic metadata, closed-set checksums and the applicable upstream
+licence/notice material, all of which are verified by the release gate.