## Feature Request: Improve Column Mode same as UltraEdit

### Description

## Feature Request: Improve Column Mode same as UltraEdit

Current NotepadNext supports basic rectangular selection by `Alt + drag mouse`, but lacks many practical column‑editing features that UltraEdit(UE) provides.
For processing fixed‑width log / CSV / structured text, UE’s column‑mode is very convenient.

### Describe the solution you'd like

P0 Must‑have：
1. Persistent toggle column‑block mode (shortcut like `Alt+C` in UE, menu entry in Edit menu, status‑bar indicator to show column‑mode is active)
2. Column insert sequential numbers (decimal/hex) in column selection
3. Column‑oriented operations: fill text into selected column block, delete whole‑column block
4. Column alignment: left‑align / right‑align / center for selected column block

P1 Nice‑to‑have:
1. Column sum for numeric values inside column selection
2. Column markers (vertical ruler line at specified column position)
3. Support find‑replace only within selected column block

### Describe alternatives you've considered

Current Alt‑drag only gives temporary selection, no dedicated column operation menu. I have to switch back to UltraEdit for these tasks.

**Additional context**
UltraEdit column‑mode doc reference: https://wiki.ultraedit.com/Column_mode
My OS: macOS

Start by tracing the existing Alt+drag rectangular-selection behavior, then inspect how Edit-menu commands and the status bar are implemented. Compare the requested P0 column-mode operations with the current selection model and define completion around persistent mode toggling, numbering, fill/delete, and alignment; the P1 items remain additional scope.

Written by the indexing model from the issue text.