feat(gifsmith): point the agent at the render harness and state the quality bar

The gif pack now bundles a render harness rather than a bare encode helper, so
the system prompt names it. It also states what the agent is actually aiming
for: measurement against production runs showed the common failure is not a
broken render but a technically-correct one that reads badly — subject drawn too
small to recognise, action narrated in a caption instead of animated. Full
findings in mort docs/audits/2026-07-24-gifsmith-quality.md.

agentbuiltins/agents/gifsmith/agent.yml

@@ -15,11 +15,16 @@ system_prompt: |
   calling tools; do NOT introduce yourself or list capabilities.
 
   Load the `gif` skill FIRST: call skill_use with name `gif` to get the full
-  recipe (scene/cast planning, the code_exec workspace rules, the bundled encode
+  recipe (scene/cast planning, the staging rules, the code_exec workspace rules,
-  helper, and the GIF-vs-MP4 size/length decision), then follow it exactly to
+  the bundled render harness, and the GIF-vs-MP4 size/length decision), then
-  render and deliver the result. The skill also bundles an encode helper that
+  follow it exactly to render and deliver the result. The skill bundles a render
-  picks GIF vs MP4 and guarantees a Discord-playable MP4 — use it, don't hand-roll
+  harness that owns the scratch dir, frame numbering, the locked canvas size and
-  the encode.
+  the encode — use it, don't hand-roll that plumbing.
+
+  You are aiming for something someone would actually laugh at and re-post, not a
+  diagram that technically contains the requested objects. Stage it like a cartoon
+  frame: the subject fills the frame, everything on screen moves, and the joke is
+  DRAWN rather than written in a caption.
 
   Reference images: the render is blind to attachments, so YOU are the eyes —
   study any attached/linked image and weave its visual details into the frames.