docs(wiki): full authoring reference and an appendix of variations

The authoring section ended on "the exact graph construction methods depend on
the Agent Framework graph shape", which is a way of not documenting them. It now
covers what the framework actually offers, checked against the source rather
than recalled.

Authoring gains: the four opt-in definition interfaces and what each declares;
WorkflowBuildContext's full surface, and the fact that BuildAsync runs once per
attempt rather than once at startup; node identity and why renaming an executor
orphans tenant gate policies; the nine built-in executors, with the three whose
behaviour surprises people called out — DelayExecutor does not sleep,
PublishEventExecutor passes through, WaitForEventExecutor runs twice; the real
edge API including conditional, fan-out, selective fan-out and fan-in barrier;
gates inline on a node with every builder method; events on a node; failure
classification; IWorkflowContext versus Runtime; both middleware seams; and the
versioning rules that bite.

Two errors found while checking against source and fixed: FailureDisposition has
no AwaitInput member (it is Retry, DeadStop, Escalate), and ExecutorBinding has
no AsExecutorBinding method (it is BindAsExecutor). Both had been written from
memory. Conditional-edge examples now use a pattern rather than a null-forgiving
dereference, since the predicate parameter is T?.

Sub-workflows turn out to be supported via Workflow.BindAsExecutor, which was
undocumented. Included, with the distinction that matters: a sub-workflow runs
inline and has no instance row, lease or event stream of its own, so an event
trigger is the tool when a genuinely independent run is wanted.

New appendix with sixteen recipes: linear, branch, fan-out/fan-in, the three
gate shapes, durable delay, HTTP, LLM, event-triggered, publish and wait, quiet
notifications, log-without-streaming, custom notifications, audit records,
custom failure classification, raw/agent/sub-workflow nodes, and registration.

Author: NinjaRocks