feat(launcher): add list + detail panel stubs (master-detail L.2)

Splits rendering into panels/list.lua and panels/detail.lua. List
implements row hit-test, scroll-state, whole-list bg-tint hook for the
dep-conflict UX (L-Q6). Detail renders an empty-state placeholder
until L.4-L.7 fill in title, description, deps, carousel, and launch
button.

panels/detail.lua

@@ -0,0 +1,37 @@
+local M = {}
+
+local PADDING = 24
+local COLOR_BG    = 0x282828FF
+local COLOR_TEXT  = 0xE0E0E0FF
+local COLOR_DIM   = 0xA0A0A0FF
+local FONT_TITLE  = 28
+local FONT_BODY   = 14
+
+function M.render(ctx)
+    local p = ctx.detail_panel_rect
+    engine.render.draw_rect(p.x, p.y, p.w, p.h, COLOR_BG)
+
+    if not ctx.selected_entry then
+        -- Empty state: background image + hint text (L.10 ships the image).
+        if ctx.bg_texture then
+            engine.render.draw_texture(ctx.bg_texture, p.x, p.y)
+        end
+        local hint = ctx.t("empty_hint")
+        local w, h = engine.render.measure_text(hint, FONT_BODY)
+        engine.render.draw_text(hint,
+            p.x + (p.w - w) / 2, p.y + (p.h - h) / 2,
+            FONT_BODY, COLOR_DIM)
+        return
+    end
+
+    -- Stub for L.4/L.5/L.6/L.7: full content lands later.
+    engine.render.draw_text(tostring(ctx.selected_entry),
+        p.x + PADDING, p.y + PADDING, FONT_TITLE, COLOR_TEXT)
+end
+
+function M.handle_click(ctx, mx, my)
+    -- Stub: real hit-tests for launch button + carousel arrows in L.5/L.7.
+    return false
+end
+
+return M