Add 4 example circuits accessible from a new toolbar dropdown:
- SR Flip-Flop (NOR) — basic set-reset latch
- SR Flip-Flop (NAND) — active-low variant
- D Latch (1-bit Memory) — gated latch with enable
- D Flip-Flop (Master-Slave) — edge-triggered with CLK
Each example shows name + description in the dropdown and loads
the full circuit with proper gate placement and wiring.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>