P0: harden FAT TCS / protection-27 smart finding

[masarray]

P0 scope

This PR hardens FAT signal finding only. It intentionally does not include the multi-IED or fascia/toolbar UX work.

Verified baseline

• TCS pathless-leaf regression is already fixed in v1.6.23 / commit 58d4b4b.
• Real FAT data also contains 7SX80 protection-27 rows with full VI3p1_27Undervoltage1/PTRC1.Op references, plus a legacy field row where 27-1 degraded to generic .Op.general while 27-2 retained its full reference.

Changes

• resolve strong exact/canonical IEC references before weak rows, independent of workbook row order;
• for weak ANSI-27 rows only, narrow candidates to explicit 27Undervoltage / PTUV IEC identities — no fuzzy text similarity;
• still require one unique remaining candidate; two unproven 27 candidates remain ambiguous and blocked;
• preserve the unique model reference proven during FAT preparation as a transient live-binding anchor, so the live phase does not re-guess a weak source row;
• clear old runtime anchors before each fresh preparation/discovery pass;
• add regression tests for full 7SX80 27 references, Siemens Application/MMS $ST$ spelling, 59/67 sibling collision protection, weak 27-1 + strong 27-2 sibling elimination, ambiguity blocking, and prepared-reference live binding.

Safety intent

The matcher remains conservative: exact/canonical references win, TCS exact-leaf behavior remains intact, and protection-27 fallback cannot select when evidence still leaves more than one candidate.

Please gate merge on the existing ARSAS build/test workflows.

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