test: restore PHP environment snippet contract

[chubes4]

Summary

• restore the exact phpEnvAssignments() smoke contract for putenv(), $_ENV, and $_SERVER
• exercise quote, newline, and backslash escaping through generated PHP
• prove invalid-name rejection and output parity between static snippet generation and phpEnvAssignmentFunction()

Root cause

#1912 / 13ccafb5 intentionally expanded static PHP environment assignment from putenv() alone to all three PHP environment surfaces, matching the runtime helper. The smoke fixture retained the old one-line expectation, so npm run check failed even though the implementation contract was correct.

Contract

For every accepted environment name and stringified value, both generation paths populate:

1. getenv() through putenv()
2. $_ENV
3. $_SERVER

Invalid names remain rejected. The test uses an escaped value containing quotes, a newline, and a backslash and compares the executable static/runtime results.

Tests

• npx tsx scripts/php-snippets-smoke.ts passes
• npx tsx tests/external-mysql-runtime-service.test.ts passes
• npm run build passes
• npm run check passes the repaired php-snippets-smoke gate and later stops at the independent artifact-patch-git-apply-smoke failure tracked by artifact-patch-git-apply-smoke expects a worktree prefix Git does not emit #2064
• adjacent independent stale fixtures discovered during verification are tracked by runtime-php-snippets test omits required environment fixture #2349 and Playground bootstrap test expects obsolete six-worker default #2350; they are intentionally out of scope

Fixes #2347