Self-host: docker-exec tar-fallback sync-back for M5 build drivers (#2963)

[PurHur]

Summary

• Fix auto --sync-back trigger matching for make bootstrap-selfhost-link and related targets (patterns no longer require a trailing space after the target name).
• Expand M5 sync-back artifact list: build/bin-compile-aot-inventory, build/selfhost, build/selfhost-lib-spine-smoke, build/selfhost-helloworld-compile, plus existing driver binaries.
• Document tar-fallback sync-back in docs/bootstrap-selfhost.md.
• Unit test guards sync-back wiring (CiScriptsTest::testDockerExecTarFallbackSyncsM5BuildDrivers).

Problem (#2963)

On harness hosts using tar-copy docker-exec, ephemeral containers dropped build/ artifacts between steps, forcing Zend gen-0 fallback in north-star5 step 4b and vendor prelink step 5.

Verification

# Pattern + sync-back (tar-fallback harness):
rm -f build/bin-compile-aot
./script/docker-exec.sh -- bash -lc 'make bootstrap-selfhost-link'
test -x build/bin-compile-aot && echo OK

# Second invocation sees host artifact:
./script/docker-exec.sh -- test -x build/bin-compile-aot

# Unit test:
./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php vendor/bin/phpunit test/unit/CiScriptsTest.php --filter testDockerExecTarFallbackSyncsM5BuildDrivers'

Closes #2963

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