feat(launcher): ship default brand assets

Solid-fill placeholders for the empty-state background (1920×1080) and
the zero-teaser hero fallback (800×450). Brand-refresh slice can drop
both files in without touching code. Loaded once on init via
engine.asset.load_texture (launcher's own sandbox).

init.lua

@@ -203,14 +203,22 @@ function init(ctx)
         list_tint          = nil,      -- nil | "warn" | "error" — set in L.4
         list_panel_rect    = nil,      -- set below from window size
         detail_panel_rect  = nil,
-        bg_texture         = nil,      -- L.10 loads it
-        default_teaser_texture = nil,  -- L.10 loads it
+        bg_texture         = nil,      -- assigned below from engine.asset.load_texture
+        default_teaser_texture = nil,  -- assigned below from engine.asset.load_texture
         t                  = nil,      -- L.8: real implementation installed below
         carousel_state     = {},       -- per-module-id state, L.5 populates
         manifest_cache     = {},       -- L.3 populates
         launcher_dir       = MODULE_DIR, -- L.4: detail.lua dofiles markdown.lua via this
     }
 
+    -- L.10: launcher-owned brand assets. Solid-fill placeholders today;
+    -- a brand-refresh slice can drop new PNGs in without touching code.
+    -- Loaded via engine.asset (the launcher's own sandbox-rooted loader),
+    -- not engine.module.load_texture — assets/launcher/ lives inside the
+    -- launcher's module dir.
+    ctx_panels.bg_texture             = engine.asset.load_texture("assets/launcher/background.png")
+    ctx_panels.default_teaser_texture = engine.asset.load_texture("assets/launcher/default_teaser.png")
+
     -- L.8: real string indirection. Looks up `key` in strings.lua, falls
     -- back to "[key]" for missing entries, and string.formats with any
     -- varargs so callers can pass format-args inline (e.g. counts).