fix: text sizing rendering — column guard, CPU optimization, preview mode

Remove hardcoded column-1 guard that broke heading placement with
display-line-numbers-mode and org-indent-mode. Headings were never
placed (placed=0 hidden=37) because posn-at-point returns terminal
columns offset by body-left, not buffer column 1.

CPU optimizations reduce position queries by 86% and heading
placements by 76%:
- Early window-range exit skips posn-at-point for off-screen overlays
- Emitted flag prevents redundant OSC 66 re-emission
- Single fold-check instead of duplicate calls
- Strip text properties to prevent org-modern payload corruption

Add preview mode that temporarily disables conflicting minor modes
(org-modern, org-appear, org-indent, visual-line, olivetti) and
unfolds all headings for clean OSC 66 rendering. Modes are restored
when heading sizes are toggled off.

Add row-based collision detection to prevent overlapping multicell
blocks when adjacent headings occupy the same terminal rows.

Deferred display property shows heading text as fallback until first
successful OSC 66 emission, preventing invisible headings.

0 files changed, 0 insertions, 0 deletions