feat(dcl): bind OPC UA nodes by namespace URI, not baked index

A stored ns=<index> reference is only meaningful against one server's namespace
table. A server that adds, removes or reorders a namespace silently re-points
every binding: best case BadNodeIdUnknown, worst case the index now names a
different namespace holding a colliding identifier and the binding resolves to
the wrong node with Good quality. Nothing could detect that, because ScadaBridge
stored no namespace URI anywhere.

OtOpcUa v3.0 makes this concrete: v2's sole custom namespace and v3's raw
namespace both sit at index 2, so v2-era bindings resolve against v3 without
error while meaning something else entirely.

Adds OpcUaNodeReference as the single translation seam between stored references
and the wire. Resolve() accepts both ns=<index>;s=<id> (existing bindings, which
keep working unchanged) and the durable nsu=<uri>;s=<id>, mapping the URI to the
live index at use time; it is wired into every parse site — subscribe, read,
write, alarm-subscribe and browse. An unpublished URI now throws naming the URI
rather than binding to whatever occupies that index, and a svr= reference to
another server is rejected instead of being resolved against the wrong address
space.

The browser emits ToDurable(), so what the picker shows is what gets stored and
newly-authored bindings are index-proof from the start. That also closes a
round-trip gap: browse previously emitted ExpandedNodeId.ToString(), which for a
URI- or server-index-carrying reference produced a string NodeId.Parse could not
read back — the same method already resolved it correctly 57 lines later.

Bindings stored before this change keep their ns= form and keep working; they are
only as durable as the server's namespace order. Re-authoring against the picker
is what makes them durable, and that re-bind still needs a live v3 rig.

Refs: Gitea #14

docs/requirements/Component-DataConnectionLayer.md

@@ -199,6 +199,10 @@ DCL is a clean data pipe on the hot path. Browse is an **opt-in capability** for
 - `DataConnectionManagerActor` handles `BrowseNodeCommand` (fields: `ConnectionName`, `ParentNodeId`, and an optional opaque `ContinuationToken` for paging) and replies with `BrowseNodeResult` (children + `Truncated` + an optional continuation token + structured `BrowseFailure?`). The Central UI facade is `IBrowseService`/`BrowseService`, backing the `NodeBrowserDialog` tag picker.
 - **Browse type-info**: each child `BrowseNode` carries optional best-effort type metadata — `DataType` (friendly name), `ValueRank` (scalar/array), and `Writable`. `DataType` is populated by **both** OPC UA and MxGateway: `RealOpcUaClient` batch-reads built-in data-type node ids and maps them to friendly names for **Variable** nodes; `MxGatewayDataConnection` surfaces each attribute leaf's `GalaxyAttribute.data_type_name` (free-form Galaxy type text) as `DataType`. `ValueRank` and `Writable` are OPC-UA-only; MxGateway leaves them unset.
 - Node ids are opaque protocol-specific strings: OPC UA uses NodeIds; MxGateway uses Galaxy gobject ids for navigable objects and full tag references for selectable attribute leaves.
+- **OPC UA namespace binding (Gitea #14)**: a NodeId's `ns=<index>` is meaningful only against one server's namespace table, so a server that adds/removes/reorders a namespace silently re-points every stored binding — best case `BadNodeIdUnknown`, worst case the index names a different namespace holding a colliding identifier and the binding resolves to the **wrong node with Good quality**. The namespace **URI** is the stable identity. `OpcUaNodeReference` is therefore the single translation seam between stored references and the wire:
+  - `Resolve(reference, session.NamespaceUris)` accepts **both** `ns=<index>;s=<id>` (existing bindings, unchanged) and the durable `nsu=<namespace-uri>;s=<id>`, mapping the URI to the live index at use time. It is used at every parse site — subscribe, read, write, alarm-subscribe, browse. A URI absent from the server's `NamespaceArray` throws with a message naming the URI, rather than binding to whatever sits at that index; a `svr=` reference to another server is rejected outright.
+  - `ToDurable(expandedNodeId, session.NamespaceUris)` is what the browser emits, so **what the picker shows is what gets stored** and newly-authored bindings are index-proof from the start. Namespace 0 is exempt (spec-fixed) and keeps its short form. It also closes a round-trip gap: the browse previously emitted `ExpandedNodeId.ToString()`, which for a URI- or server-index-carrying reference produced a string `NodeId.Parse` could not read back.
+  - Bindings stored before this change keep their `ns=` form and keep working; they are only as durable as the server's namespace order. Re-authoring against a picker (which now emits `nsu=`) is what makes them durable — see `docs/plans/` and Gitea #14 for the OtOpcUa v3.0 cutover, where v2's sole custom namespace and v3's `raw` namespace both sit at index 2, so v2-era bindings resolve against v3 without error while meaning something else.
 - Browse runs against the live session; no caching at DCL.
 - **Frame-size guard**: the reply crosses the site→central Akka frame (default 128 KB) on a temp Ask actor; an oversized reply is silently discarded by remoting, hanging the picker. The child handler caps each `BrowseNodeResult` to a byte budget (~100 KB) before replying, OR-ing the adapter's own truncation signal into `Truncated`. This is protocol-agnostic (every adapter's reply funnels through it). Per-protocol upstream caps narrow the window first: OPC UA requests at most 500 references per node (continuation point → `Truncated`); MxGateway relies on the gateway's `BrowseChildren` page cap.
 - **`BrowseNext` paging** (OPC UA): a `Truncated` level no longer forces manual node-id entry. When the OPC UA browse is truncated, the adapter returns the session's continuation point as the reply's opaque `ContinuationToken`; a follow-up `BrowseNodeCommand` carrying that token calls `Session.BrowseNext` to fetch the next page (the picker exposes this as **"Load more"**). Continuation points are session-bound and can expire — `BadContinuationPointInvalid` is caught and the browse restarts from a fresh first page rather than failing. Manual node-id entry remains as a fallback when the site or its session is offline.