feat(manager): receive and preview V4 shadow plans without dispatch

docs/netplan-v4-receiver.md

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+# V4 plan reception and local preview (observation only)
+
+This module does not execute a battery command. The existing regulator and its
+setpoints remain unchanged. `NetzfahrplanAktiv` must remain false.
+
+The optional `NetzfahrplanV4EmpfangAktiv` property defaults to false. When enabled
+with the existing shadow sender, one bounded GET is made before the next native
+operation POST, avoiding reading the plan immediately after queuing its replan.
+A successful inspection acknowledges `shadow_seen` once per plan/step. This is
+not `applied`. An HTTP failure clears the local preview; it does not change the
+old control mode or its connection credentials.
+
+The V4 service must first support `receiverProtocolVersion=1`, installation IDs
+in envelope and plan, per-input event references, and the stable controlContext
+used at calculation time. Old or cross-plant responses are deliberately refused.
+The client checks fresh/lastRun/pending status, exact configuration revision,
+model-family registry, known price coverage, contiguous half-open five-minute
+intervals, asset mapping and power balance. Numerical feasibility checks are
+not evidence of economic performance or permission to control devices.
+
+A cache watchdog refreshes the diagnostic display every 10 seconds, without any
+network requests. Cached response older than 90 seconds, plan older than 900
+seconds, an expired step, invalid local measurement or policy change invalidates
+the preview. Missing targets are JSON null and '-' in the display, never zero.
+Restart/ApplyChanges clears the cache. Existing control functions are not edited.
+
+The preview is currently limited to ONE battery. Multiple batteries are still
+accepted by the server planner; local allocation is explicitly unsupported in
+this stage. Preview feedback uses actual grid and battery power, local capacity,
+available power, minimum/maximum SOC, discharge hysteresis, network-charging
+permission and import/export/month limits. It exposes any remaining grid-limit
+violation instead of pretending the battery can resolve it. It is a momentary
+calculation only, NOT the commissioned real-time regulator. PV curtailment and
+external SDL/base-load separation must still be validated before any live test.
+
+Two read-only variables below the manager expose a HTML summary and detailed
+JSON. No EnableAction, consumer RequestAction, SendData or actor property writes
+are used. The existing form.json and web portal assets are not modified.
+
+Offline checks:
+
+    php tests/V4Receiver/protocol_checks.php
+    php tests/V4Receiver/receiver_checks.php
+
+The PHPUnit wrapper runs these in separate subprocesses, so fake IPS and curl
+functions cannot contaminate other module tests. The mocked transport uses no
+real credentials or connections. Full Symcon kernel testing and installation
+are separate commissioning steps; these unit tests are not field acceptance.