feat: add multi-engine regex flavour support

public/engines/README.md

@@ -1,13 +1,42 @@
 # Engine assets
 
 Regex Tools executes ECMAScript through the browser's native `RegExp` engine.
-It also ships three declared, self-hosted runtime packs:
+It also ships ten declared, self-hosted runtime packs:
 
-- `pcre2/`: official PCRE2 10.47, 8-bit WebAssembly;
-- `python/`: Pyodide 314.0.3 with CPython 3.14.2 `re`; and
+- `pcre2/`: official standalone PCRE2 10.47, 8-bit WebAssembly;
+- `php/`: PHP 8.5.8 `preg_*` through `@php-wasm/web-8-5` 3.1.46; this runtime
+  reports PCRE2 10.44;
+- `perl/`: Perl 5.28.1 through the legacy WebPerl 0.09-beta prebuilt runtime;
+- `python/`: Pyodide 314.0.3 with CPython 3.14.2 `re`, a complete linked
+  base-runtime inventory (including vendored loader ports),
+  preferred-form/patch manifest and independently pinned legal closure;
+- `ruby/`: minimal ruby.wasm 2.9.3-2.9.4 with CRuby 4.0.0 `Regexp`;
 - `java/`: TeaVM 0.15.0's `java.util.regex` class library compiled to an
-  ES2015 module. This module is not OpenJDK.
+  ES2015 module; this module is not OpenJDK;
+- `cpp/`: Emscripten 6.0.4 libc++ `std::wregex`, with an exact traced native
+  component/source/legal manifest;
+- `go/`: Go 1.26.5 standard-library `regexp` for `js/wasm`;
+- `rust/`: Rust `regex` crate 1.13.1 for `wasm32-unknown-unknown`; and
+- `dotnet/`: .NET 10.0.10 `System.Text.RegularExpressions` for browser
+  WebAssembly.
+
+The selectable Scala/JVM compatibility profile intentionally shares
+`java/`. It does not contain or claim a Scala runtime.
 
 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.
+The Python pack's `SOURCE-MANIFEST.json` records exact source archives or Git
+trees, both vendored stack-parser source ports, all Pyodide
+CPython/Emscripten patches and the evidence for every component already linked
+into its loader or base WebAssembly module. The C++ source manifest similarly
+binds its exact module to the traced Emscripten runtime, musl, emmalloc,
+compiler-rt, libc++ and libc++abi inputs and the explicit non-selection of
+libunwind. The
+hundreds of optional entries in `pyodide-lock.json` are a package catalogue;
+their wheels are not part of this pack.
+
+The Perl pack remains an explicit exception in age, not in identity: its
+upstream beta assets are retained byte-for-byte and labelled legacy everywhere.
+Its loader contains a dormant optional JavaScript-interoperability `eval` site;
+the fixed bridge does not import or call it.