feat: RandR, monitor hotplug #1

Move all monitor detection, setup, and hotplug handling from main.zig
to monitor.zig to improve code organization and maintainability.
- Reduced main.zig from ~1800 to 1220 lines
- Created monitor module with init() function for dependency injection
- Moved setupMonitors, RandR/Xinerama detection, and hotplug handlers
- Updated main.zig to use mon.* function calls
- No functional changes, build verified

please investigate more, the fix looks ugly

Replace unsafe i16 casts with proper i32 handling throughout monitor
initialization. Screen dimensions from X11 can exceed i16 range (32767px),
which would cause panics. The Monitor struct already uses i32 internally,
so accepting i32 parameters in createMonitor() and updateMonitorGeometry()
aligns types and eliminates casting risk.
Increase maximum supported monitors from 16 to 64, with clear warning
messages when the limit is exceeded. This provides visible diagnostics
instead of silently dropping additional displays.
Remove restrictive validation that rejected large screen dimensions,
as this conflicts with the expanded i32 coordinate space.
Fix type mismatches in monitor geometry comparisons by removing i16
casts and comparing i32 values directly.
Changes:
- Change createMonitor/createMonitorRandR to accept i32 coordinates
- Change updateMonitorGeometry to accept i32 dimensions
- Count connected outputs before allocation for diagnostics
- Increase output buffer from 16 to 64 entries
- Add warning when output count exceeds maximum
- Remove unsafe integer casts at all call sites
- Fix i32/i16 type mismatch in geometry comparison logic
- Remove screen dimension range validation that was too restrictive

Add proper error checking and diagnostic logging for critical X11 resource
initialization failures during setup:
- XftDrawCreate: Validate drawable creation and log display/visual/colormap
 state on failure. Return XftDrawCreationFailed error instead of panicking
 with a null pointer dereference.
- XCreateGC: Check graphics context creation and log error with context
 creation details. Return GraphicsContextCreationFailed error.
- XCreateFontCursor: Validate both bar cursor and root cursor creation.
 Return CursorCreationFailed error instead of proceeding with invalid
 cursor (0).
These changes prevent crashes from X11 initialization failures and provide
clear diagnostic information for debugging display/visual/colormap issues.

Replace XClearWindow with XFillRectangle to properly clear the root
window background when switching to tags with no visible clients.
XClearWindow doesn't override existing background pixmaps from the
display manager, while XFillRectangle directly draws the background color.
Also initialize all monitors during setup() to fix background rendering
on the initial tag.

because working on a laptop that has the same resolution as the xephyr
window is a PITA

Only dispatch RandR event handling when event type is actually a RandR
event. Remove debug logging and the overly broad catch-all handler that
would trigger monitor updates on unrecognized RandR subtypes.