fix(hashline): enforce hashline_read before hashline_edit

[randomm]

Summary

• Adds FileTime.hashlineRead() and FileTime.assertHashlineRead() to track which files have been read via hashline_read specifically
• hashline_edit now requires a prior hashline_read call (not just any read), preventing agents from calling it after a plain read with no anchors
• Fixes namespace shadowing bug in time.ts where local variable shadowed outer function
• Adds cross-session isolation test confirming Session A's read doesn't grant Session B edit permission

Fixes #321