improve(hashline-edit): rewrite tool description with examples and fix lines schema

- Add XML-structured description (<must>, <operations>, <examples>, <auto>)
- Add 5 concrete examples including BAD pattern showing duplication
- Add explicit anti-duplication warning for range replace
- Move snapshot rule to top-level <must> section
- Clarify batch semantics (multiple ops, not one big replace)
- Fix lines schema: add string[] to union (was string|null, now string[]|string|null)
- Matches runtime RawHashlineEdit type and description text

src/tools/hashline-edit/tools.ts

@@ -30,7 +30,7 @@ export function createHashlineEditTool(): ToolDefinition {
             pos: tool.schema.string().optional().describe("Primary anchor in LINE#ID format"),
             end: tool.schema.string().optional().describe("Range end anchor in LINE#ID format"),
             lines: tool.schema
-              .union([tool.schema.string(), tool.schema.null()])
+              .union([tool.schema.array(tool.schema.string()), tool.schema.string(), tool.schema.null()])
               .describe("Replacement or inserted lines as newline-delimited string. null deletes with replace"),
           })
         )