docs(DV-6): document Debug View tabbed-tree layout, native placeholders, and new AlarmStateChanged fields

- Component-CentralUI.md: replace flat-table Debug View section with tabbed
  tree layout (Attributes + Alarms tabs, TreeView<TItem> reuse, hierarchy from
  canonical names, branch roll-up, all-configured-alarms rule, native source
  binding nodes with quiet-binding placeholder rows, per-leaf rendering detail)
- Component-SiteRuntime.md (Instance Actor Wiring): add idle-binding placeholder
  emission via BuildAlarmStatesSnapshot(), _nativeAlarmKinds map, and
  NativeSourceCanonicalName stamping on live native events
- Component-SiteRuntime.md (Enriched AlarmStateChanged): document two new
  additive fields — NativeSourceCanonicalName (string?) and
  IsConfiguredPlaceholder (bool) — plus their gRPC proto fields 22/23 and
  StreamRelayActor/SiteStreamGrpcClient pack/unpack
- Component-Commons.md (Attribute Stream DTOs): extend AlarmStateChanged bullet
  with the same two additive fields and proto field numbers

docs/requirements/Component-SiteRuntime.md

@@ -281,6 +281,8 @@ The Instance Actor owns native-alarm setup alongside its computed Script and Ala
 - **Spawning**: for each entry in `_configuration.NativeAlarmSources`, the Instance Actor spawns a `NativeAlarmActor`. Spawning is **skipped when there is no DCL manager** (e.g., debug/test contexts with no data connections), since native alarms require a live source subscription.
 - **Kind derivation**: the `AlarmKind` passed to each `NativeAlarmActor` is derived from the bound connection's protocol — `Mx*` protocols → `NativeMxAccess`, otherwise → `NativeOpcUa`.
 - **Latest-event retention**: the Instance Actor retains the latest enriched `AlarmStateChanged` per alarm name in `_latestAlarmEvents`. The DebugView snapshot is built from this map so it carries the **unified condition view plus native metadata** for both computed and native alarms. Computed alarms that have not yet produced an event fall back to a **Normal projection** so the snapshot is complete.
+- **Idle native source binding placeholders**: `BuildAlarmStatesSnapshot()` additionally emits one placeholder `AlarmStateChanged` for each configured native alarm source binding that currently has **no live conditions** in `_latestAlarmEvents`. The placeholder has `IsConfiguredPlaceholder = true` and carries the binding's canonical name in `NativeSourceCanonicalName`. The Instance Actor maintains a `_nativeAlarmKinds` map (`sourceCanonicalName → AlarmKind`) populated at spawn time to stamp the correct `Kind` on each placeholder. This ensures the Debug View Alarms tab shows every configured binding as a tree node even when quiet.
+- **`NativeSourceCanonicalName` on live events**: every `AlarmStateChanged` emitted by a `NativeAlarmActor` stamps its source binding's canonical name in `NativeSourceCanonicalName`. The Debug View uses this field to place each live condition under the correct native-source binding node in the tree.
 - **Reset semantics**: `_latestAlarmEvents` and the mirrored native state are cleared on redeploy/undeploy (same trigger as static-override reset) but rehydrate from SQLite on failover.
 
 ---
@@ -304,6 +306,10 @@ The `AlarmStateChanged` message published by both Alarm Actors and Native Alarm
 - **`Condition`** (`AlarmConditionState`): the unified condition view. Computed alarms supply a computed default; native alarms carry the mirrored source condition.
 - **Native metadata** (populated for native alarms; defaulted/empty for computed): `SourceReference`, `AlarmTypeName`, `Category`, `OperatorUser`, `OperatorComment`, `OriginalRaiseTime`, `CurrentValue`, `LimitValue`.
 - **Computed-alarm projection**: computed alarms are surfaced as **auto-acknowledged** with `Severity = Priority`, so a single enriched shape carries both computed and native alarms onto the stream and into the DebugView snapshot.
+- **`NativeSourceCanonicalName`** (`string?`): the canonical name of the native alarm source binding a native condition belongs to (e.g. `Motor1.NativeAlarms`). `null` for computed alarms. Stamped by the `NativeAlarmActor` on every emitted event; also carried on idle-binding placeholder rows emitted by the Instance Actor.
+- **`IsConfiguredPlaceholder`** (`bool`): `true` for a synthetic row emitted by the Instance Actor to represent a configured native source binding that currently has no live conditions. These rows are never persisted or forwarded as operational alarms — they exist solely so the Debug View can render every configured binding as a tree node. `false` on all other rows.
+
+Both fields are **additive-only** (init-only with defaults: `null` / `false`) and are mirrored additively on the gRPC `AlarmStateUpdate` proto as fields 22 (`native_source_canonical_name`, `string`) and 23 (`is_configured_placeholder`, `bool`). `StreamRelayActor` and `SiteStreamGrpcClient` pack/unpack these fields without touching existing fields, preserving backward compatibility across version-skew boundaries.
 
 The enriched message flows Instance Actor → site-wide Akka stream → `SiteStreamManager` → `SiteStreamGrpcServer` and is streamed to central as the gRPC `AlarmStateUpdate` event (see [Component-Communication.md](Component-Communication.md)).