fix(hashline-edit): improve hash computation and tool description clarity

- Include line number in hash computation to ensure uniqueness
- Add explicit examples of WRONG vs CORRECT LINE:HASH format
- Clarify that hash must be hex characters (0-9, a-f only)
- Update tests to use dynamic hash computation

src/tools/hashline-edit/hash-computation.ts

@@ -1,8 +1,9 @@
 import { HASH_DICT } from "./constants"
 
-export function computeLineHash(_lineNumber: number, content: string): string {
+export function computeLineHash(lineNumber: number, content: string): string {
   const stripped = content.replace(/\s+/g, "")
-  const hash = Bun.hash.xxHash32(stripped)
+  const hashInput = `${lineNumber}:${stripped}`
+  const hash = Bun.hash.xxHash32(hashInput)
   const index = hash % 256
   return HASH_DICT[index]
 }