fix(ext-api): correct NodeMode doc-comments to match LGraphEventMode

Per AUDIT-LG.4 finding: the previous doc-comments had numeric values
mapped to wrong names (claimed 1=Never, 2=Bypass, 3=once, 4=trigger,
but the actual LiteGraph runtime enum is 0=ALWAYS, 1=ON_EVENT,
2=NEVER, 3=ON_TRIGGER, 4=BYPASS). An extension following the old
docs and writing setMode(3) for 'execute once' would actually wire
the dead ON_TRIGGER plumbing.

Also notes that slots 1 and 3 are legacy ABI-reserved positions for
the dead trigger/action subsystem flagged for removal by AUDIT-LG.5.

Cross-ref: research/architecture/audit-litegraph-pruning.md
\xc2\xa7AUDIT-LG.4 \xc2\xa7AUDIT-LG.5

src/extension-api/node.ts

@@ -53,11 +53,22 @@ export type Size = [width: number, height: number]
 /**
  * LiteGraph node execution mode.
  *
- * - `0` — Always execute.
- * - `1` — Never execute (muted).
- * - `2` — Bypass (passthrough).
- * - `3` — Execute once.
- * - `4` — Execute on trigger.
+ * Numeric values match `LGraphEventMode` in the LiteGraph runtime.
+ *
+ * - `0` — `ALWAYS`: execute every run (default).
+ * - `1` — `ON_EVENT`: legacy slot for the dead trigger/action subsystem;
+ *   has no behavioural effect in the current scheduler. Reserved for ABI
+ *   compatibility — do not use in new extensions.
+ * - `2` — `NEVER`: muted; node is skipped during execution.
+ * - `3` — `ON_TRIGGER`: legacy slot for the dead trigger/action subsystem;
+ *   gated behind `LiteGraph.do_add_triggers_slots` (always `false`). Reserved
+ *   for ABI compatibility — do not use in new extensions.
+ * - `4` — `BYPASS`: passthrough; inputs are forwarded to outputs without
+ *   running the node.
+ *
+ * Practical extension code should use `0` (always) or `2` (never/muted) or
+ * `4` (bypass). Slots `1` and `3` are documented for completeness but their
+ * runtime semantics are pending the AUDIT-LG trigger-subsystem cleanup.
  *
  * @stability stable
  */