Implement Semantic Consolidator V0

- add deterministic canonicalization support for extraction items
- add facts-only semantic consolidation using local Ollama
- preserve source evidence and validate complete fact coverage
- add conservative merge rules and non-LLM tests
- record the first validated real-life consolidation benchmark
- document current scope, limitations and next evaluation step

samples/benchmarks/semantic_consolidator_v0/report.md

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+# Semantic Consolidator V0 Report
+
+- Scope: facts only
+- Model: `qwen3.5:9B`
+- LLM call count: 1
+- Runtime: 390.119 seconds
+- Fact item count: 33
+- Prompt characters: 15393
+- Estimated prompt tokens: 3849
+- Prompt eval count: 4295
+- Eval count: 2344
+- Merged fact groups: 1
+- Source facts involved in merges: 2
+- Singleton fact groups: 31
+- Validation: passed
+- Output path: `samples/benchmarks/semantic_consolidator_v0/consolidated_extractions.json`
+
+## Actual Merges
+
+### Der Leiter F&E führt die Projektliste auf dem zweiwöchentlichen Schnittstellen-Stand-Up.
+
+- Source fact IDs: fact_0025, fact_0031
+- Merge reason: Semantic equivalence: Both items state that the Head of R&D leads the project list at the bi-weekly interface stand-up meeting. The difference in wording ('auf den' vs 'auf dem') and minor elaboration on defining project types does not change the core factual proposition regarding who performs which action when.
+- Review decision: accepted as correct.