Add editor actions module composing maps write APIs

paint_cell_at, erase_cell_at, cycle_rotation, save plus thin
wrappers for the UI hit-tests (set_active_layer/_atlas/_tile,
toggle_layer_visible/_roof_mode/_picker). Each action updates
state and delegates the actual map mutation to lib-core.maps.

src/actions.lua

@@ -0,0 +1,86 @@
+-- src/actions.lua
+-- High-level edit operations. Combines state mutations with lib-core.maps writes.
+
+local maps  = require("lib-core.maps")
+local state = require("src.state")
+
+local M = {}
+
+-- =====================================================================
+-- Cell painting
+-- =====================================================================
+
+function M.paint_cell_at(cell_x, cell_y)
+    if state.is_roof_mode() then
+        maps.set_roof(cell_x, cell_y, 1)
+    else
+        local gid = maps.encode_gid(
+            state.get_active_atlas(),
+            state.get_active_tile(),
+            state.get_active_rot()
+        )
+        maps.set_cell_gid(state.get_active_layer(), cell_x, cell_y, gid)
+    end
+    state.mark_dirty()
+end
+
+function M.erase_cell_at(cell_x, cell_y)
+    if state.is_roof_mode() then
+        maps.set_roof(cell_x, cell_y, 0)
+    else
+        maps.set_cell_gid(state.get_active_layer(), cell_x, cell_y, 0)
+    end
+    state.mark_dirty()
+end
+
+-- =====================================================================
+-- Hotkey-driven actions
+-- =====================================================================
+
+function M.cycle_rotation()
+    state.cycle_rotation()
+end
+
+function M.save()
+    local id   = state.get_map_id()
+    local path = state.get_map_path()
+    if not id or not path then
+        engine.print("map-editor: cannot save — no map loaded")
+        return
+    end
+    maps.save_to_disk(id, path)
+    state.mark_clean()
+    engine.print(string.format("map-editor: saved '%s' to %s", id, path))
+end
+
+-- =====================================================================
+-- UI-driven actions (called by ui.lua hit-tests)
+-- =====================================================================
+
+function M.set_active_layer(layer_name)
+    state.set_active_layer(layer_name)
+end
+
+function M.toggle_layer_visible(layer_name)
+    state.toggle_layer_visible(layer_name)
+end
+
+function M.toggle_roof_mode()
+    state.toggle_roof_mode()
+end
+
+function M.set_active_atlas(atlas_idx)
+    state.set_active_atlas(atlas_idx)
+    -- Reset to first tile of the new atlas
+    state.set_active_tile(1)
+end
+
+function M.set_active_tile(tile_id)
+    state.set_active_tile(tile_id)
+end
+
+function M.toggle_picker()
+    state.toggle_picker_open()
+end
+
+return M