Add PHP converter with lossless round-trip support

[MelbourneDeveloper]

TLDR

Adds a PHP DTO ↔ typeDiagram converter (8th language) that losslessly round-trips the canonical HOME_PAGE_SAMPLE, and wires PHP into the web converter playground.

Details

New

• packages/typediagram/src/converters/php.ts — 564-line converter emitting final readonly class DTOs with constructor-promoted public params, declare(strict_types=1), PHPStan @template / @param list<...> / @param array<K,V> / |null docblocks, and sealed interface + implementing classes with @var 'Kind' tags for tagged unions. Parser supports nested generics, Option unwrapping, @typediagram-kind alias wrappers, and scan-state tracking for //, /* */, and string literals inside class bodies.
• packages/typediagram/test/converters/php.test.ts — 12 tests across four describe blocks: [CONV-PHP-TO-COMPLEX], [CONV-PHP-FROM], [CONV-PHP-RT], and [CONV-PHP-EDGE].
• PHP tab in the web playground — added to the LANGUAGES list, LANG_LABELS, highlight rules (PHP_RULES covering class/interface keywords, ?type nullables, $vars, PHPDoc), and both convertSource / convertFromTd converter maps.

Changed

• converters/index.ts exports php.
• Language union in converters/types.ts gains "php".
• Web SupportedLang aligned across converter.ts, converter-render.ts, and converter-highlight.ts.

Known lossless limitation

Option<Unit> is NOT round-trippable because both Unit and Option<Unit> collapse to PHP null native type with no docblock — the nullability is indistinguishable on parse. HOME_PAGE_SAMPLE does not use Option<Unit>, so the byte-for-byte round-trip test still holds. Documented inline in the edge-case test.

How Do The Automated Tests Prove It Works?

• [CONV-PHP-RT] losslessly round-trips the home-page example through PHP (TD text preserved) — the canonical expectLosslessRoundTrip(php) assertion (identical pattern to the other 7 converters) confirms TD → PHP → TD is byte-for-byte identical, including field order (which required removing the sortFields Option-reordering hack in the emitter).
• [CONV-PHP-TO-COMPLEX] asserts specific emitted strings: final readonly class, @template T, public ?string $label, @param list<string>, @param array<string, int>, interface Shape, @var 'Circle', @implements Result<T>, @typediagram-kind alias.
• [CONV-PHP-FROM] covers alias-only parsing and the NO_SUPPORTED_DEFINITIONS error path.
• [CONV-PHP-EDGE] covers empty constructors, Option<List<Int>> / Option<Map<String,Int>> emission and parse, private-promoted params being skipped, inline // / /* */ / string-literal tolerance, and $kind mismatch handling.
• Full suite: make ci green — 318 tests pass, bundle 74.55 KB within 75 KB budget, coverage 95.17% lines / 91.2% branches (above 95 / 90.89 thresholds); php.ts specifically at 96.2% / 92.16%.

Co-authored with @voku (original PHP converter work from the php branch).

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