docs: add input-and-placement OpenSpec change and update AGENTS.md

Plan input handling and pattern placement before Game of Life mechanics:
keyboard bindings config, mouse placement with preview/rotation,
HiDPI scaling, and cell grid. Update AGENTS.md project notes.

openspec/changes/input-and-placement/proposal.md

@@ -0,0 +1,34 @@
+# Proposal
+
+## Why
+
+wlgol currently renders an animated stripe pattern and has no Game of Life state, no input handling beyond Escape, and no HiDPI awareness. Before implementing the automaton, the application needs a usable interaction layer: configurable keyboard bindings, mouse-driven placement of patterns with a live preview, and rendering that stays crisp on scaled displays. This change establishes that layer so later GoL mechanics can build on it.
+
+## What Changes
+
+- Add configurable keyboard bindings loaded from `~/.config/wlgol/keys.conf` (TOML), merged over built-in defaults, with modifier-aware matching (Ctrl/Shift/Alt/Super).
+- Extend keyboard handling to report active modifiers and dispatch bound actions (`quit`, `cancel`, `rotate`, `select:<pattern>`, `clear`, `pause`, `step`, `speed_up`, `speed_down`, `toggle_grid`).
+- Implement mouse tracking and click handling: selecting a tool shows a rotating preview that follows the cursor; `Space` rotates 90°; left click places the pattern (tool stays armed); `Esc` cancels.
+- Add a cell grid (8 logical px per cell, wall boundary) with storage, resize-with-preserve, and rendering of alive cells.
+- Add four built-in patterns (Glider, Blinker, Block, Toad) with rotation support.
+- Add HiDPI scaling (fractional via `wp_fractional_scale` + `wp_viewporter`, fallback to `wl_output.scale`) with logical/physical coordinate conversion.
+- Auto-generate a default `keys.conf` on first run if missing.
+
+## Capabilities
+
+### New Capabilities
+
+- `keyboard-bindings`: configurable, modifier-aware key-to-action mapping with defaults and TOML override.
+- `pattern-placement`: tool selection, live preview, rotation, click placement, cancellation.
+- `display-scaling`: fractional and integer HiDPI scaling with logical/physical conversion.
+- `cell-grid`: grid storage, resize handling, wall boundary, alive-cell rendering.
+
+### Modified Capabilities
+
+None.
+
+## Impact
+
+- Affected code: `wlgol.c`, `tkeyboard.c/h`, `tpointer.c/h`; new modules `config`, `grid`, `pattern`, `scale`, `render`.
+- New dependency: vendored `tomlc99` for TOML parsing; generated Wayland protocols `viewporter` and `fractional-scale-v1`.
+- Config I/O under `~/.config/wlgol/`; no public API changes.