refactor(hashline): change content separator from colon to pipe

Change LINE#HASH:content format to LINE#HASH|content across the entire
codebase. The pipe separator is more visually distinct and avoids
conflicts with TypeScript colons in code content.

15 files updated: implementation, prompts, tests, and READMEs.

src/tools/hashline-edit/validation.ts

@@ -115,7 +115,7 @@ export class HashlineMismatchError extends Error {
 
       const content = fileLines[line - 1] ?? ""
       const hash = computeLineHash(line, content)
-      const prefix = `${line}#${hash}:${content}`
+      const prefix = `${line}#${hash}|${content}`
       if (mismatchByLine.has(line)) {
         output.push(`>>> ${prefix}`)
       } else {