Document Cloud Agent driver and site-simulator layout

[frahlg]

Accepted text proposal

Issue or Discussion: documentation-only

Maintainer comment that accepted this scope: Cloud Agent environment setup; record how device-drivers and device-simulator fit the test stack.

What changed

Adds a Cursor Cloud specific instructions section to AGENTS.md. It states that this environment is a multi-repo FTW stack, that driver edits belong in srcfl/device-drivers (not ftw/drivers/*.lua), and that srcfl/device-simulator is the site FTW talks to for protocol-shaped integration. make e2e / make dev still use the in-tree Go simulators.

No runtime behaviour changes.

Why

Cloud Agents were treating make dev as the only site path, and ftw/drivers as editable source. That is wrong: the recovery snapshot is generated, and a real-site loop for driver/protocol work goes through device-simulator (Sungrow hybrid + bound SDM630).

Evidence from this environment: FTW on :8080 with both drivers ok, Sungrow PV ≈ −2.5 kW, SDM630 as site meter, ticks advancing against device-simulator on :8762.

Boundaries and safety

Out of scope: changing make dev, e2e, or FTW config defaults. Stale site-meter data still stops dispatch. Planner output is still not sent to hardware. The in-tree Go simulators remain the make e2e path.

Verification

• Started device-simulator server mode (:8762, Modbus 5100+)
• Created Sungrow-hybrid inverter + bound SDM630 site
• FTW GET /api/health → drivers_ok: 2, status: ok
• GET /api/status → sungrow pv_w ≈ −2550, bat_soc 0.5, sdm630 status: ok, tick counts advancing
• make test-driver ID=sungrow in device-drivers → 85 passed, 4 skipped
• Start script is idempotent (second run: “FTW already running”)
• A human does not need to review UI; no UI changed

Checklist

• The diff implements one accepted scope and does not add follow-on work.
• I checked open pull requests that touch the same files.
• Tests cover the changed behaviour and its failure path. (docs-only; live stack verified as above)
• A human reviewed every changed web/UI view in a browser, or no UI changed.
• A Changeset is included, or the change is exempt.
• Every commit has a DCO sign-off.