refactor(jcode): fold three reverse-scan copies into one, reuse the shared hook POST

The jcode journal reader, the Claude transcript reader and the Command Code
transcript reader each carried their own copy of the same reverse chunked line
scan; they now share one tested helper. jcode's managed hook script drops its
hand-rolled curl for buildPosixAgentHookPostCommand, which also gains it the
raw-JSON transport and the --noproxy guard the bespoke copy was missing.

Co-authored-by: czzczz <chanzrz_zbf@foxmail.com>

src/main/jcode/hook-gate-script.test.ts

@@ -105,10 +105,10 @@ describe.runIf(process.platform !== 'win32')('jcode managed hook as jcode runs i
       const script = readFileSync(scriptPath, 'utf8')
       const gateBranch = script.slice(script.indexOf('if [ "$JCODE_HOOK_EVENT" = pre_tool ]'))
       expect(gateBranch).toContain('orca_post_jcode_event >/dev/null 2>&1 &')
-      // The observer path keeps the plain call, so a slow POST cannot be lost to
-      // a script that exited first.
+      // The observer path keeps the foreground call, so a slow POST cannot be lost
+      // to a script that exited first.
+      expect(gateBranch).toContain('orca_post_jcode_event >/dev/null 2>&1 || :')
       expect(script.trimEnd().endsWith('exit 0')).toBe(true)
-      expect(script).toContain('\norca_post_jcode_event\n')
     } finally {
       cleanup()
     }