M1: edit tool with opencode's replacer chain, ported verbatim

Ports opencode's multi-strategy string-replacer chain (and its test table) into harness-tools::edit, giving the edit tool the same fuzzy-match fallback behavior opencode relies on.

crates/harness-tools/src/lib.rs

@@ -1,4 +1,5 @@
 mod bash;
+mod edit;
 mod glob;
 mod grep;
 mod paths;
@@ -6,6 +7,7 @@ mod read;
 mod write;
 
 pub use bash::BashTool;
+pub use edit::EditTool;
 pub use glob::GlobTool;
 pub use grep::GrepTool;
 pub use read::ReadTool;
@@ -15,10 +17,11 @@ use std::sync::Arc;
 
 use harness_core::tool::ToolRegistry;
 
-/// Registers the M1 built-ins (`edit` is added separately once its replacer chain lands).
+/// Registers all M1 built-ins: read, write, edit, bash, glob, grep.
 pub fn register_builtins(registry: &mut ToolRegistry) {
     registry.register(Arc::new(ReadTool));
     registry.register(Arc::new(WriteTool));
+    registry.register(Arc::new(EditTool::new()));
     registry.register(Arc::new(BashTool));
     registry.register(Arc::new(GlobTool));
     registry.register(Arc::new(GrepTool));