refactor(nodes): let the product own its node families

[endrix]

Stacked on #35. Pairs with wfpy-ide's declaration PR — the platform stops holding these and the product starts supplying them, so they land together.

The problem

The platform coloured nodes by reading annotations named agent, tool, viewer and source, and held an accent colour and an icon for each:

--workflow-color-task-agent:      #e87d40;
--workflow-color-external-tool:   #b26dff;
--workflow-color-external-viewer: #49a6b8;
--workflow-color-external-agent:  #ff6f91;
--workflow-color-external-source: #4fa97a;

Those are one product's decorator names. The other shell's vocabulary is actor and network — it matches none of them, so every one of its nodes drew in the default graphite. A platform that knows one product's taxonomy renders every other product's graph plain, and nothing reports it: the colours simply never match.

The neutrality gate didn't catch it because it greps for product names. agent and viewer are innocent words individually; it's the set that is one product's, and no grep sees a set.

What moves, what stays

task and network stay — every dataflow graph has nodes and subgraphs. The annotation-derived families move to the profile as data: annotation, colour, icon. The class is derived (external-actor-<id>), so core names no family, and the CSS is generated the way contributed palette icons already are.

Two things the move had to keep

Order decides. A node can carry the annotation that makes it openable and the one that says what it is. A source carries both — so without a declared order it is painted as the node it is the opposite of.

A family can be narrowed by an annotation argument. A @tool(cmd="python") showed a script icon rather than a terminal; that was a hardcoded special case reading scriptInterpreterCommands. It is now two declared families sharing one annotation, split by match and told apart by id.

Dead code found on the way

Nothing has ever set cal:hasExternalMembers — declared and read, never written — so the icon it selected and the actor-node-agent class it drove could not appear. header-task-agent had no producer either. Both were keyed on the same borrowed vocabulary.

Tests

14 new for the seam, plus the existing server tests updated to declare families like a profile does. Mutation-checked:

mutation	caught
declaration order ignored	3 failed
match condition ignored	2 failed
quotes not stripped from the matched value	2 failed
id ignored for the class name	1 failed
icon CSS emitted for a family without one	1 failed
unsafe family name accepted	1 failed
unsafe colour accepted	1 failed

The generated CSS reproduces the removed rules selector-for-selector and colour-for-colour; I diffed the output against what was deleted.

Gates: typecheck 5/5, neutrality 4/4, full suite green (851 tests), bundle builds.

Not in scope, but noted

viewer-mouse-listener still keys double-click on an annotation named viewer, and the create-node wizard still lists @tool / @agent by name. Same class of coupling, different seam — worth a follow-up rather than widening this one.