Fix fragment diagram absolute positioning

Accounts for center alignment and parent width of 95%
Move Octocat watermark to upper left

Prevents opaque diagrams from cover branding and only partially showing.
Fix diagram fragment styling, cleanup, and alignment correction
Update Merge recursive diagram with flat look
Update Merge fast-forward diagram with flat look
Add AI source "flat look" diagrams
Revise Fast Forward Merge final step as clean-line graph
Update Rebase branch diagram with flat look
Update Rebase Interactive diagram with flat look
Update Remotes diagram with flat look
Update Commit Three Stage Thinking diagram with flat look
Update Diff diagrams with flat look
Update States of Tracking diagrams with flat look
Merge branch 'gh-pages' into diagram-update-theme-fix

Reverse merge to update out-of-date branch.
Reverse merge to resolve out-of-date conflicts
Refine Rm-Mv flat-look diagram with clearer state transitions
Update Rm-Mv diagram with two visual examples

Add Rm-Mv State of Tracking simple diagram flat look and change
title to thorough step-through "map" of tracking states.
Add additional build-step for Commit Three Stage diagram
Remove deprecated Fast Forward diagram
Remove deprecated Rebase diagram