Laguna: actionable thinking guidance + setup verification (follow-through on #2)

[TheTom]

Completes the response to @Defilan's field notes in #2. The substantive corrections from that issue (§5e, the §2 enable_thinking fix, the §5b ablation, and the cross-model note in patterns.md) already landed on main. This PR is the part that was still missing for a reader.

The problem this fixes

Correcting enable_thinking had a knock-on I didn't handle at the time: it left the guide's top recommendation without a usable instruction. "Thinking OFF" was recommendation #1, and the setting everyone reaches for to do it turns out to be a no-op. A reader following the guide literally could not perform step one.

What's here

• "How to actually minimize thinking", ranked by evidence: never send enable_thinking: true (the one setting that provably changes the template), use a named professional persona (best-evidenced lever, three stacks, 6/6 vs 0/5 single-turn), expect attenuation not elimination in long agentic loops, and cap your own tokens as the backstop. Carries the honest caveat that whether this stops the model reasoning or only stops reasoning being parsed is unresolved and stack-dependent.
• "Verify your setup (worth 5 minutes)", four checks for the traps that are all silent: tool calls actually parse (the 83% to 0% cliff), -fa on, what your stack does with reasoning_content, and revision pinned + capped. That third check exists precisely because all three known stacks behave differently there, so the guide now tells readers to measure their own rather than trust any published rate, ours included.
• Quickstart says three stacks, not two.
• Card synced. Its thinking and serving rows were still asserting things the guide no longer claims. PNG re-rendered.

Why the verification block earns its space

Nearly every problem reported with this model across three independent stacks has turned out to be configuration rather than capability, and every one of those failure modes is silent: chatml degrades tool calls to prose without erroring, flash-attention-off just looks like a slow model, enable_thinking: false looks like it worked, and config drift looks like the model regressed. Five minutes of checks up front is cheaper than any of those diagnoses.

Closes #2.