fix(extraction): detect export-macro-annotated class in .h language check (#1159)

[colbymchenry]

Carries @luoyxy's #1133 forward onto current main (rebased to resolve conflicts with the UE work — #1158 and the #1206 dense-header guard — that landed after #1133 was opened; the fix itself in grammars.ts was unchanged and auto-merged).

Fixes #1159.

The bug

A .h file defaults to C and is only reclassified as C++ when looksLikeCpp finds a C++-specific construct. That check couldn't see through an export/visibility macro: in class ENGINE_API UFoo : public UObject the macro sits between class and the type name, so the macro-blind \bclass\s+\w+\s*[:{] branch failed to match. A lean Unreal-Engine header carrying only that macro-annotated class plus GENERATED_BODY() — no public: / virtual / namespace / template to fall back on — was therefore parsed as C. The C extractor has classTypes: [] and no export-macro pre-parse, so the class definition and its inheritance edge silently vanished, quietly undoing the macro-class recovery from #1061.

Note: the issue's literal minimal repro has a public: inside the body, which already trips the existing heuristic → detects cpp. The true failing shape is the lean header (no other C++ signal), which this PR targets.

The fix

One alternation branch added to looksLikeCpp, mirroring the exact shape blankCppExportMacros already recovers:

\b(?:class|struct)\s+[A-Z][A-Z0-9_]+\s+\w+\s*(?:final\s*)?[:{]

The macro shape [A-Z][A-Z0-9_]+ is identical to blankCppExportMacros (c-cpp.ts) — so the exact set of headers this routes to cpp is precisely the set the C++ path then recovers (no "routes to cpp but still collapses" gap). The two-token <keyword> <MACRO> <Name> before a [:{] never occurs in valid C, so genuine C headers are unaffected.

Verified (on current main)

Header (.h)	before	after
class ENGINE_API UFoo : public UObject + GENERATED_BODY(), no public:	c ❌	cpp ✓
struct ENGINE_API FBar : public FBase {};	c ❌	cpp ✓
class MYMODULE_API FFoo { (brace next line, no base)	c ❌	cpp ✓
C guards (struct Point {…}, struct FOO bar;, struct FOO getFoo(){, enum COLOR{…}, struct FOO x = {5}, typedef struct FOO T;)	c	c ✓ (unchanged)

Test plan

• New regression test in __tests__/extraction.test.ts (macro class, macro struct w/ inheritance, brace-next-line, plus a genuine-C guard)
• npx vitest run __tests__/extraction.test.ts — 579 passed
• npx tsc --noEmit clean

🤖 Generated with Claude Code