fix: Validate restored sessions and fix inline preview autocmd leak

[mhiro2]

Summary

• Validate session items read from disk before restoring so a single corrupt entry no longer aborts the whole restore
• Harden normalize_range as the validation chokepoint for untrusted data, coercing corrupt ranges to safe defaults
• Fix a leak where the inline preview's once close-event autocmds stayed armed after close()

Changes

• 254f06b : fix(persist): validate session items and ranges restored from disk
  • Type-check each item (uri string / range table) in the restore loop and isolate it in pcall so one corrupt entry cannot abort restoring the rest of the session
  • Count only items that actually produce a popup as restored, so the skipped-item warning, PeekstackRestore item_count, and on_done result reflect the real outcome
  • Add type validation to normalize_range, coercing non-table range/start/end and non-numeric line/character to safe defaults
• 31a4d64 : fix(ui): clear inline preview augroup on close to prevent autocmd leak
  • Delete the PeekstackInlinePreview augroup in close() so the remaining once close-event autocmds are disarmed when one of them fires, instead of staying armed and triggering on unrelated later activity