Web: FastCGI record codec + VM listener (#173)

[PurHur]

Summary

• Implements FastCGI 1.0 record framing and PARAMS name-value codec under lib/Web/FastCgi/ (issue Web: FastCGI request loop adapter (nginx / php-fpm compatible) #173 slice 1).
• Adds bin/fcgi.php and phpc fcgi for VM serving over TCP; RequestHandler maps PARAMS → CGI env and runs CgiDriver::runVmScript (slice 2).
• Slice 3: FCGI_KEEP_CONN multiplex — multiple requests per connection (php-fpm keep-alive parity).
• Slice 4: --binary flag routes through CgiAotDriver::runCapture() for native AOT binaries (Web: AOT CGI wrapper for phpc-built binaries (production nginx spawn) #665 pattern).
• Slice 4 tests: FastCgiTest::testAotFastCgiHealthReturnsOk + testAotFastCgiPathInfoDiagnostics behind FASTCGI_WEB_AOT_SMOKE_GATE=1.
• PHPUnit: FastCgiRecordTest (binary fixtures), FastCgiTest (009-FastCGIWeb health + keep-alive multiplex + AOT, @group serve).

php-src reference

• php/php-src sapi/fpm/fpm/fpm_main.c — FastCGI request loop
• php/php-src main/fastcgi.c — FCGI_KEEP_CONN
• Reuses CGI param semantics from Web: AOT CGI wrapper for phpc-built binaries (production nginx spawn) #665 (CgiDriver, CgiAotDriver, Superglobals)

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit test/unit/FastCgiRecordTest.php test/unit/FastCgiTest.php'
# 8 tests OK (VM + record codec; AOT tests skipped without gate)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && FASTCGI_WEB_AOT_SMOKE_GATE=1 vendor/bin/phpunit test/unit/FastCgiTest.php --filter testAotFastCgi'
# 2 tests OK (AOT health + PATH_INFO via FastCGI)

Remaining on #173

• FASTCGI_SMOKE_GATE CI wiring (CI: FASTCGI_SMOKE_GATE opt-in in ci-local after #173 lands #1899)

Part of #173