feat: effort dial + storyboard — end the plugin's economy mode

[HeyRenan]

Why

The plugin under-delivered by default ("economy mode"): the instruction surface told the agent to pick the lowest-effort artifact, forbade coherent rich flows ("never stack two concepts"), and disabled its own judgment ("you are a low-capability executor") — with no line ever permitting richness. Great capability, timid output.

What

• Effort dial — quick / standard / rich / cinematic, requestable in any language; absent a request, the default is now rich so a first render impresses with zero config. Effort scales the craft poured into the right artifact — it never forces a bigger artifact than the subject needs (one element → a polished still, not a movie).
• Storyboard — before recording a flow, the agent states the beats in plain language; proceeds by default, waits for a nod at cinematic or on request.
• Rebalance — default rich not lowest; a coherent multi-step flow is one narrative; motion composition is the agent's judgment (easing/counts still come from the tables); added the missing permission "richness that explains is not filler". Every technical guardrail (--dry, render mode, label anchoring, shrink-before-deliver) is unchanged.

Instruction-only — no scripts touched.

Validation (blind A/B)

Two context-free subagents each read the real committed skill (old on main, new on this branch) and produced a reel for the same request, with no bias injected:

• old skill → flow reel, reasoning "pick the lowest-effort… default to a still unless a flow".
• new skill → richer flow reel, reasoning "absent a request, default to rich" + the "never forces a bigger artifact" clamp.
• Decision-only agents also confirmed: the dial scales (still → movie → hero → showcase), a button at rich stays a still (not a movie), and the old skill forbids the storyboard while the new one shows it.

Sanity: --dry + no-bleed tests pass.

Bump 1.5.0 → 1.6.0 (minor: new effort + storyboard capability).