feat(build): preserve unrelated ConfigDumpInfo entries after successful target-scoped build

[korolevpavel]

Split from #24 on 2026-07-26.

Implement an opt-in build.configDumpInfoStrategy: preserve-unrelated contract. After a successful /UpdateDBCfg, reconcile platform-generated ConfigDumpInfo.xml only for metadata roots affected by the target-scoped build, preserving the byte representation and baseline entries outside that scope.

Acceptance criteria:

• strategy is opt-in, validated, documented, and represented in config schema;
• reconcile runs only after successful UpdateDBCfg;
• unexpected/unrelated entries are rejected rather than silently accepted;
• no UUID or configVersion values are invented; sources are baseline and successful platform output only;
• BOM, EOL, terminal newline, and unaffected XML bytes are preserved;
• target-root mapping and nested metadata behavior have focused regression tests.

Out of scope: failure/cancellation rollback; that is tracked in #24.