feat(php): PHP type inference and method-call/chained resolution

[vitali87]

Context

Structural PHP support is in place and covered by tests (functions incl. anonymous/arrow, classes/interfaces/traits/enums, calls, imports, inheritance edges, and oracle tests for containment/structure/span). This issue tracks the remaining gap toward full parity with Java: PHP-specific type inference and method-call resolution.

Gap

There is no parsers/php/ resolver subpackage analogous to parsers/java/ (which has type inference, method resolution, and inheritance-aware lookups). As a result, PHP method calls on typed receivers and chained accesses are not resolved to precise CALLS edges the way Java's are.

Unsupported / imprecise today:

• Inferring $var types from new X(), typed parameters, typed properties, and method return types.
• Resolving instance method calls $obj->method() to the declaring class.
• Resolving chained access $obj->field->method() and fluent chains $obj->a()->b().
• Walking the inheritance chain (extends/implements/trait use) so inherited members resolve.
• self::, static::, parent:: and ::class resolution.

Proposed work

Add a codebase_rag/parsers/php/ resolver mirroring the Java approach:

• Build a per-scope variable type map (locals, params, properties).
• Resolve method/static calls against the receiver type, walking class/interface/trait inheritance.
• Emit CALLS edges for resolved instance, static, and chained calls.
• Add a PHP test suite for these resolution cases (RED/GREEN), following the existing test_php_* style.

Split off from #108, where the structural support was confirmed complete.