docs: add gol-simulation OpenSpec change

Plan Game of Life mechanics: Conway rules, pause/resume, stepping,
speed control, and paused-only cell editing with drag painting.

openspec/changes/gol-simulation/proposal.md

@@ -0,0 +1,29 @@
+# Proposal
+
+## Why
+
+The application now supports input, pattern placement, and HiDPI rendering, but has no Game of Life dynamics. This change adds the actual automaton: Conway's rules, pause/resume, single stepping, speed control, and mouse editing of cells, so the tool becomes usable for exploring patterns.
+
+## What Changes
+
+- Add Conway's Game of Life simulation that updates the cell grid on a timer.
+- Start paused by default; allow pause/resume, single-step, and speed changes.
+- Allow mouse editing of cells (left click sets alive, right click sets dead) only while paused, including drag painting.
+- Add default key bindings for pause (`p`), step (`n`), and speed (`+`/`-`).
+- Render simulation state and reflect pause/editing in the UI (via stdout status).
+
+## Capabilities
+
+### New Capabilities
+
+- `gol-simulation`: Conway rules, tick timing, pause/resume, stepping, speed control, and paused-only editing.
+
+### Modified Capabilities
+
+None.
+
+## Impact
+
+- Affected code: `wlgol.c`, `grid.c/h` (read during ticks), possibly new `simulation.c/h`.
+- Reuses existing input/config infrastructure; no new dependencies.
+- Config defaults updated with simulation keys.