feat(map-editor): mode-pill 3 segments for Auto/Cell/Direct

MODE_PILL_W widens 130 -> 195 (3 x 65). mode_pill_layout returns
the new cell segment between auto and direct; draw_mode_pill
iterates the new triple; the click-handler dispatches the cell
segment to actions.set_mode("cell-tile"). Self-test t9 confirms
the three segments sit at consecutive SEG_W offsets.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

init.lua

@@ -387,7 +387,7 @@ local ui = (function()
     -- Menu bar
     local MENU_BAR_H           = 24
     local MENU_LABEL_PAD_X     = 12
-    local MODE_PILL_W          = 130
+    local MODE_PILL_W          = 195
     local MODE_PILL_H          = 18
     local MODE_PILL_SEG_W      = 65
     local MODE_PILL_MARGIN     = 4
@@ -668,21 +668,26 @@ local ui = (function()
         local y = (MENU_BAR_H - MODE_PILL_H) / 2
         return {
             x = x, y = y,
-            auto   = { x = x,                    y = y, w = MODE_PILL_SEG_W, h = MODE_PILL_H, mode = "auto-tile" },
+            auto   = { x = x,                       y = y, w = MODE_PILL_SEG_W, h = MODE_PILL_H, mode = "auto-tile" },
-            direct = { x = x + MODE_PILL_SEG_W,  y = y, w = MODE_PILL_SEG_W, h = MODE_PILL_H, mode = "direct" },
+            cell   = { x = x + MODE_PILL_SEG_W,     y = y, w = MODE_PILL_SEG_W, h = MODE_PILL_H, mode = "cell-tile" },
+            direct = { x = x + MODE_PILL_SEG_W * 2, y = y, w = MODE_PILL_SEG_W, h = MODE_PILL_H, mode = "direct" },
         }
     end
 
     local function draw_mode_pill()
         local lay = mode_pill_layout()
         local current = state.get_mode()
-        for _, seg in ipairs({ lay.auto, lay.direct }) do
+        for _, seg in ipairs({ lay.auto, lay.cell, lay.direct }) do
             local active = (current == seg.mode)
             local bg     = active and COL_BUTTON_BG_ACTIVE or COL_BUTTON_BG
             local fg     = active and COL_TEXT_ACTIVE      or COL_TEXT
             engine.render.draw_rect(seg.x, seg.y, seg.w, seg.h, rgba(bg, 0xFF))
             engine.render.draw_rect_lines(seg.x, seg.y, seg.w, seg.h, rgba(COL_BUTTON_BORDER, 0x40))
-            local label = (seg.mode == "auto-tile") and "Auto-Tile" or "Direct"
+            local label
+            if     seg.mode == "auto-tile" then label = "Auto-Tile"
+            elseif seg.mode == "cell-tile" then label = "Cell-Tile"
+            else                                label = "Direct"
+            end
             engine.render.draw_text(label, seg.x + 8, seg.y + 3, 11, rgba(fg, 0xFF))
         end
     end
@@ -1310,7 +1315,7 @@ local ui = (function()
 
         -- Mode-pill
         local pill = mode_pill_layout()
-        for _, seg in ipairs({ pill.auto, pill.direct }) do
+        for _, seg in ipairs({ pill.auto, pill.cell, pill.direct }) do
             if in_rect(mx, my, seg.x, seg.y, seg.w, seg.h) then
                 if button == "left" then
                     actions.set_mode(seg.mode)
@@ -1444,6 +1449,8 @@ local ui = (function()
     M._VIEW_ITEMS      = VIEW_ITEMS
     M._EDIT_ITEMS      = EDIT_ITEMS
     M._LAYER_PANEL_ROWS = LAYER_PANEL_ROWS
+    M._mode_pill_layout = mode_pill_layout
+    M._MODE_PILL_SEG_W  = MODE_PILL_SEG_W
 
     return M
 end)()
@@ -1560,6 +1567,17 @@ local function self_test()
     engine.test.equals(state.get_mode(), "cell-tile",
         "t8: set_mode('cell-tile') sets mode")
 
+    -- t9: mode_pill_layout returns 3 segments at consecutive x positions
+    local pill = ui._mode_pill_layout and ui._mode_pill_layout() or nil
+    engine.test.assert(pill ~= nil,
+        "t9: mode_pill_layout accessible from self_test")
+    engine.test.assert(pill.cell ~= nil and pill.direct ~= nil,
+        "t9: pill has all three segments (auto, cell, direct)")
+    engine.test.equals(pill.cell.x - pill.auto.x, ui._MODE_PILL_SEG_W,
+        "t9: cell segment sits one SEG_W right of auto")
+    engine.test.equals(pill.direct.x - pill.cell.x, ui._MODE_PILL_SEG_W,
+        "t9: direct segment sits one SEG_W right of cell")
+
     -- t12: cycle_mode cycles auto -> cell -> direct -> auto
     state.set_mode("auto-tile")
     state.cycle_mode()