Add per-entity merge audit trail

Adds ResolutionStrategy enum and EntityAudit struct to track how each
entity was resolved during merge (unchanged, diffy_merged, inner_merged,
conflict variants, etc). Exposed via --audit flag on weave-driver (writes
JSON sidecar) and new weave_merge_audit MCP tool.

Author: rs545837

Cargo.lock

@@ -9,6 +9,7 @@ sem-core = { git = "https://github.com/Ataraxy-Labs/sem", version = "0.3" }
 diffy = "0.4"
 thiserror = "2"
 tempfile = "3"
+serde = { version = "1", features = ["derive"] }
 
 [dev-dependencies]
 pretty_assertions = "1"

crates/weave-core/Cargo.toml

@@ -1,4 +1,5 @@
 use std::fmt;
+use serde::Serialize;
 
 /// The type of conflict between two branches' changes to an entity.
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -384,7 +385,7 @@ fn parse_conflict_header(header: &str) -> (String, String, ConflictComplexity, S
 }
 
 /// Statistics about a merge operation.
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone, Default, Serialize)]
 pub struct MergeStats {
     pub entities_unchanged: usize,
     pub entities_ours_only: usize,

crates/weave-core/src/conflict.rs

@@ -6,5 +6,5 @@ pub mod region;
 pub mod validate;
 
 pub use conflict::{parse_weave_conflicts, ParsedConflict};
-pub use merge::{entity_merge, entity_merge_with_registry, MergeResult};
+pub use merge::{entity_merge, entity_merge_with_registry, EntityAudit, MergeResult, ResolutionStrategy};
 pub use validate::{validate_merge, ModifiedEntity, SemanticWarning};