Complete rewrite from glyph-based (v14) to buffer-relative design:
- ns_ax_buffer_text() with BUF_BEGV/ZV/PT, 100KB cap
- EmacsAccessibilityBuffer (AXTextArea per window)
- EmacsAccessibilityModeLine (AXStaticText per mode line)
- Enum fix: Edit=0, SelectionMove=1
- Text cache by BUF_MODIFF
- Tree rebuild on window config change only
- Minibuffer included
- Zoom code preserved (UAZoomChangeFocus)
- 1142 lines (nsterm.h +47, nsterm.m +1017)
