Add weighted candidate scoring (role + name + proximity)

[JE-Chen]

anchor_locator is a single spatial relation + distance sort and ab_locator races whole strategies by elapsed time — neither is a weighted multi-signal scorer that ranks ambiguous candidates by role match + fuzzy name similarity + anchor proximity + enabled-state.

• score_candidates (AC_score_candidates): returns ScoredCandidates (element / score / matched_on breakdown) best-first; each active signal contributes 0..1 and the score is their mean. Name similarity is injectable, defaulting to the project's fuzzy_ratio (reused — no new string-distance code).
• best_candidate (AC_best_candidate): the top one (or None).
• Pure-stdlib over element dicts; powers self-heal / grounding when several boxes could be the target. Fully headless-testable (exact-near-anchor ranks first, disabled+wrong-role last, injected similarity used). Wired through all 5 layers + headless test + EN/Zh docs + WHATS_NEW. Qt-free.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 31 complexity · 2 duplication

Metric	Results
Complexity	31
Duplication	2

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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