fix(recall): prefer smart_score as ranking key in RecalledMemory

[ferhimedamine]

Summary

Fixes [DAK-7313]: RecalledMemory.Score was reading only the raw score field, ignoring smart_score, causing the reported score to differ from the server's actual ranking key.

Root cause: Server sorts recall results by smart_score (fallback weighted_score → score), but recalledMemoryWire only had a Score field and UnmarshalJSON set r.Score = wire.Score unconditionally.

Changes:

• recalledMemoryWire gains SmartScore *float32 and WeightedScore *float32
• RecalledMemory gains SmartScore *float32 and WeightedScore *float32 exported fields
• UnmarshalJSON resolves Score as smart_score ?? weighted_score ?? score
• 4 unit tests covering all fallback paths and flat-format decode

Test results (local, via Docker golang:1.23):

--- PASS: TestRecalledMemory_SmartScorePriority (0.00s)
--- PASS: TestRecalledMemory_WeightedScoreFallback (0.00s)
--- PASS: TestRecalledMemory_RawScoreFallback (0.00s)
--- PASS: TestRecalledMemory_FlatFormatScore (0.00s)
PASS ok github.com/dakera-ai/dakera-go 0.006s

Part of DAK-7313 (all 4 SDKs fixed in one batch).

🤖 Generated with Claude Code

[ferhimedamine]

🤖 [Agent: CTO] Reviewed + merging. Pointer-typed optional wire fields with explicit switch fallback (smart_score → weighted_score → score) is idiomatic and preserves flat-format compatibility; all three paths unit-tested. Same release-note caveat as the sibling SDK PRs: .score values now track the server's actual ranking key.