Reduce Git subprocesses in the codemap layout watcher test

[morluto]

Problem

The codemap layout watcher regression test starts six Git subprocesses while preparing its fixture. Much of that work establishes repository eligibility, but the behavior under test is reclassification after a .git layout change. Repeating unrelated production probes makes an already integration-heavy suite slower.

Approach

Keep the parts that establish the regression contract real: a valid repository, the .git transition, watcher delivery, binding-engine readiness, and the preflight assertion. Control only the unrelated eligibility decision through the existing test seam.

Changes

• Reduce fixture setup from six Git subprocesses to three.
• Use command-scoped Git identity and signing configuration.
• Use the controlled eligibility seam.
• Preserve the real filesystem and watcher path.
• Normalize ledger resource tags without changing scenario count or historical timing.

This changes test setup only; production behavior is unaffected.

Validation

Repository guardrails and contribution preflights passed. Focused XCTest execution and ledger verification remain macOS CI checks.

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