docs(readme): lead with trading, keep the watchdog case underneath

[AetherAI3]

README-only. No code changes.

Two things at once: the hero rewrite from the distribution push, and the watchdog/compliance material that had been sitting uncommitted in the working tree since the earlier positioning pass. Rather than discard either, trading leads and the general case follows in the same document.

Hero

Before	A deterministic DSL for replayable, host-governed decision rules.
After	Trading and agent rules that run the same way every time — with a receipt.

The old line is accurate and names nobody with a problem. It also opens with three abstract nouns, which is roughly two seconds of a topic-page visitor's attention spent on vocabulary.

A real rule now sits above the fold — the MaxDrawdownBreaker from nano/library/risk/, comment header trimmed:

strategy MaxDrawdownBreaker {
    agent RiskDesk
    every 1m {
        if DRAWDOWN >= 5 {
            pause()
        }
    }
}

Chosen deliberately over an entry signal: it emits PAUSE and escalates to a named agent, so it demonstrates the host-governance separation directly and carries no directional or performance implication.

DSL, IR and host-governed all stay — in the body, where readers who want that vocabulary will find them. They just aren't the front door.

Structure

• Start with the strategy library moves up, to sit directly after Quick start. It is the section that makes the product concrete, and it was fourth.
• Watchdog / compliance / audit-evidence / explainable-automation land after Small by design — trading first, general case underneath.

Every other section is unchanged and still present.

Verification

tests/test_docs.py compiles every fenced nano block in the repo's markdown, so a README example that doesn't compile fails CI. All three blocks introduced or moved here were checked against the compiler before landing:

Block	Result
MaxDrawdownBreaker	compiles → PAUSE
TrustedRouteWatchdog	compiles → PAUSE, OBSERVE
ReleaseCompliance	compiles → PAUSE, OBSERVE

The marked <!-- README-EXAMPLE --> block guarded by tests/test_readme_example.py is untouched.

Full suite: 378 passed, 2 skipped.

Claims check

No performance, return, win-rate, or backtested figures anywhere. The framing that Nano proposes an Intent and the host decides whether to act is kept prominent — it's true, and it's what keeps the project clear of anything resembling investment advice. The strategy library keeps its "conformance corpus, not a performance claim" disclaimer.