Make match ranking deterministic and strengthen visual-hint regressions

[Djain912]

Summary

This PR improves matcher determinism, regression protection, and CLI documentation around positional snapshot fields.

What changed

• Added a shared deterministic comparator for scored matches.
• Made combined strategy merging stable by preserving input order before sorting.
• Applied the same deterministic tie-break behavior to embedding ranking.
• Added regression tests for tie scenarios in combined and embedding strategies.
• Added a regression test to ensure "sign in" is not treated as a visual-layout hint.
• Expanded CLI snapshot docs to clearly show supported geometry/positional fields used by visual hints.

Why

Equal-score candidates could produce unstable ordering, which can cause flaky behavior across repeated runs. This change makes tie outcomes predictable and test-backed.

Validation

• go test ./... (passes)

Risk

Low. Behavior changes are scoped to tie-breaking and deterministic ordering.

Reviewer Checklist

• Verify deterministic ordering behavior for equal-score candidates.
• Confirm both combined and embedding strategies use the shared tie-break policy.
• Confirm non-tie ranking behavior is unchanged.
• Review new regression tests for tie cases and visual query parsing.
• Validate CLI docs for positional/geometry fields match parser support.
• Confirm no unrelated scratch files are included in the PR.