fix(csharp): resolve chained static-factory calls Foo.Create().Bar() (#750) (#753)

A C# method called through a static factory or fluent chain —
`Foo.Create().Bar()`, `JObject.Parse(s).Property(...)`,
`Instant.FromUtc(...).InZone(zone)` — lost the receiver's type, so the chained
method didn't resolve and the call was invisible to callers/impact/trace. Ports
the #645/#608 mechanism to C# (additive, like Java #751):

- Part 1: capture C# return types in the extractor, reading the `returns` field
  (`static Foo Create()` -> `Foo`); predefined/array/generic/nullable/namespaced
  types are normalized or skipped.
- Part 2: encode a chained `member_access_expression` receiver
  (`Foo.Create(args).Bar()`) as `inner().Bar` with normalized empty parens, so
  factory calls that take arguments still split. Non-chained member calls keep
  their existing `recv.Method` text.
- Part 3: resolve via the shared matchDottedCallChain (now Java/Kotlin/C#),
  validated by resolveMethodOnType so a wrong inference yields NO edge.

Known limitation (safe): C# extension-method chains don't resolve, since the
method lives on the extension class, not the receiver's type — no edge, never a
wrong one.

Validated: synthetic decoy + args + absent-method safety tests; full suite green;
real-repo A/B on Newtonsoft.Json (945 .cs: +3, 0 lost) and nodatime (488 .cs:
+73, 0 lost) — node count identical (no explosion), 0 edges lost, precision
spot-checked verbatim (Instant.FromUtc().InZone(), Offset.FromHoursAndMinutes().Plus(),
OffsetDateTimePattern.CreateWithInvariantCulture().WithTwoDigitYearMax()).
EXTRACTION_VERSION 7 -> 8.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -29,6 +29,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
+- C# method calls made through a static factory or fluent chain now resolve to the correct class. A call like `Foo.Create().Bar()` or `JObject.Parse(s).Property(...)` used to lose the receiver's type, so the chained method didn't resolve and the call was invisible to callers/impact/trace. CodeGraph now captures C# return types and infers the chained receiver's type from what the inner call returns, creating the edge only when that class genuinely has the method (so a wrong inference produces no edge). Existing C# indexes should be re-indexed (`codegraph index -f`) to benefit. (#750) (C#)
 - Kotlin method calls made through a companion-object factory or fluent chain now resolve to the correct class. A call like `Foo.getInstance().bar()` or `Config.create(opts).build()` used to drop the receiver entirely, so the chained method silently attached to a same-named method on an unrelated class — or didn't resolve at all — corrupting callers, impact, and trace. CodeGraph now captures Kotlin return types and infers the chained receiver's type from what the inner call returns, creating the edge only when that class genuinely has the method (so a wrong inference produces no edge instead of a misleading one). Existing Kotlin indexes should be re-indexed (`codegraph index -f`) to benefit. (#750) (Kotlin)
 - Java method calls made through a static factory or fluent chain now resolve to the correct class. A call like `Foo.getInstance().bar()` or `Config.create(opts).build()` used to lose the receiver's type, so when two classes had a same-named method the call silently attached to whichever was indexed first — or didn't resolve at all — corrupting callers, impact, and trace. CodeGraph now captures Java return types and infers the chained receiver's type from what the inner call returns, creating the edge only when that class genuinely has the method (so a wrong inference produces no edge instead of a misleading one). Covers factories and fluent builders that take arguments (`hashKeys().arrayListValues()`), including builders that return a nested type. Existing Java indexes should be re-indexed (`codegraph index -f`) to benefit. (#750) (Java)
 - PHP: a method called through a chained static factory — `Cls::for($x)->method(...)`, the canonical Laravel per-credential / per-tenant client idiom — now records a caller edge. Previously the receiver type (what `for()` returns) was never recovered, so `codegraph_callers` returned nothing for the method and the call was invisible to `codegraph_impact`. CodeGraph now captures PHP return types — `: self` / `: static` resolve to the declaring class, `: SomeClass` to that class — and resolves the chained method on the factory's result, creating the edge only when that class actually has the method (so a wrong inference produces no edge). Existing PHP indexes should be re-indexed (`codegraph index -f`) to benefit. Thanks @cvanderlinden. (#608) (PHP)