feat: add Game of Life simulation mechanics

Implement Conway rules with tick timing, pause/resume, single stepping,
speed control, and paused-only cell editing with drag painting. Update
default key bindings for pause/step/speed. Mark verification complete.

openspec/changes/gol-simulation/tasks.md

@@ -2,20 +2,20 @@
 
 ## 1. Simulation core
 
-- [ ] 1.1 Implement Conway tick using a second grid buffer and swap, verifying a known pattern (blinker) oscillates.
-- [ ] 1.2 Add tick timing in the frame loop with adjustable interval, verifying ticks occur at configured rate.
+- [x] 1.1 Implement Conway tick using a second grid buffer and swap, verifying a known pattern (blinker) oscillates.
+- [x] 1.2 Add tick timing in the frame loop with adjustable interval, verifying ticks occur at configured rate.
 
 ## 2. Controls
 
-- [ ] 2.1 Wire pause/step/speed actions to simulation state, verifying pause stops ticks and step advances one generation.
-- [ ] 2.2 Add default key bindings for p/n/+/- and verify config tests pass.
+- [x] 2.1 Wire pause/step/speed actions to simulation state, verifying pause stops ticks and step advances one generation.
+- [x] 2.2 Add default key bindings for p/n/+/- and verify config tests pass.
 
 ## 3. Editing
 
-- [ ] 3.1 Implement paused-only cell editing on left/right click, verifying clicks change cell state only when paused.
-- [ ] 3.2 Implement drag painting while paused, verifying drag sets/clears cells.
+- [x] 3.1 Implement paused-only cell editing on left/right click, verifying clicks change cell state only when paused.
+- [x] 3.2 Implement drag painting while paused, verifying drag sets/clears cells.
 
 ## 4. Verification
 
-- [ ] 4.1 Build and run ctest, verifying all tests pass.
-- [ ] 4.2 Manual run: verify pause, step, speed, editing, and Esc.
+- [x] 4.1 Build and run ctest, verifying all tests pass.
+- [x] 4.2 Manual run: verify pause, step, speed, editing, and Esc.