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/list.lua

@@ -0,0 +1,82 @@
+local M = {}
+
+local PADDING = 16
+local ROW_HEIGHT = 56
+local ROW_GAP = 4
+local COLOR_BG          = 0x202020FF
+local COLOR_ROW         = 0x303030FF
+local COLOR_ROW_HOVER   = 0x404040FF
+local COLOR_ROW_ACTIVE  = 0x505080FF
+local COLOR_TEXT        = 0xE0E0E0FF
+local COLOR_DIM         = 0xA0A0A0FF
+local FONT              = 18
+
+-- Returns the rect rect-table {x,y,w,h} of the row for entry index i.
+function M.row_rect(ctx, i)
+    local p = ctx.list_panel_rect
+    return {
+        x = p.x + PADDING,
+        y = p.y + PADDING + (i - 1) * (ROW_HEIGHT + ROW_GAP) - ctx.scroll_y,
+        w = p.w - 2 * PADDING,
+        h = ROW_HEIGHT,
+    }
+end
+
+-- Pick the display label per spec L-Q8: summary || name || id.
+local function label_for(entry)
+    return entry.summary or entry.name or entry.id
+end
+
+function M.render(ctx)
+    local p = ctx.list_panel_rect
+    -- Apply whole-list bg tint per L-Q6 if conflicts exist.
+    local bg = COLOR_BG
+    if ctx.list_tint == "warn"  then bg = 0x4A3A1AFF end
+    if ctx.list_tint == "error" then bg = 0x4A1A1AFF end
+    engine.render.draw_rect(p.x, p.y, p.w, p.h, bg)
+
+    -- News row pinned on top.
+    if ctx.news_entry then
+        local rect = {
+            x = p.x + PADDING, y = p.y + PADDING - ctx.scroll_y,
+            w = p.w - 2 * PADDING, h = ROW_HEIGHT,
+        }
+        local col = (ctx.selected_entry == "news") and COLOR_ROW_ACTIVE or COLOR_ROW
+        engine.render.draw_rect(rect.x, rect.y, rect.w, rect.h, col)
+        engine.render.draw_text(ctx.news_entry.title or "News",
+            rect.x + PADDING, rect.y + PADDING, FONT, COLOR_TEXT)
+        ctx.news_entry.rect = rect
+    end
+
+    for i, entry in ipairs(ctx.module_entries) do
+        local rect = M.row_rect(ctx, i + (ctx.news_entry and 1 or 0))
+        if rect.y + rect.h >= p.y and rect.y <= p.y + p.h then
+            local col = COLOR_ROW
+            if ctx.selected_entry == entry.id then col = COLOR_ROW_ACTIVE end
+            engine.render.draw_rect(rect.x, rect.y, rect.w, rect.h, col)
+            engine.render.draw_text(label_for(entry),
+                rect.x + PADDING, rect.y + PADDING, FONT, COLOR_TEXT)
+        end
+        entry.rect = rect
+    end
+end
+
+function M.handle_click(ctx, mx, my)
+    if ctx.news_entry and engine.spatial.aabb_contains_point(ctx.news_entry.rect, mx, my) then
+        ctx.selected_entry = "news"
+        return true
+    end
+    for _, entry in ipairs(ctx.module_entries) do
+        if entry.rect and engine.spatial.aabb_contains_point(entry.rect, mx, my) then
+            ctx.selected_entry = entry.id
+            return true
+        end
+    end
+    return false
+end
+
+function M.handle_scroll(ctx, dy)
+    ctx.scroll_y = math.max(0, ctx.scroll_y - dy * 24)
+end
+
+return M