feat(ui): the type hierarchy — what a type is built on, and what dispatches through it (CG-58)

A vertical tree above the members outline for classes, interfaces, structs,
traits, protocols, enums, unions and type aliases: ancestors above (the whole
chain, not just the direct parent), the focus in accent, subtypes below indented
per level. `extends` draws solid, `implements` dashed; a synthesized edge — Go's
implicit interface satisfaction — draws dashed wider and carries the site it was
wired at, so a relation the resolver inferred never reads like one the source
wrote down. For an interface the fan below IS the set of runtime targets a call
can land on, and a type with eight or more implementers leads with that in a
sentence. Members that redeclare an ancestor's are marked in the outline.

The walk lives in `src/graph/type-hierarchy.ts`, following CG-50/CG-51: shared
computation in `src/graph/`, presentation in the caller. Its `countImplementers`
is now also what `ToolHandler.buildPolymorphicBoundaries` counts with, so "N
types implement X" is the same N whether an agent reads it or a person does.
`/api/node` carries the block as `hierarchy` rather than a second endpoint —
it is part of the Symbol view's first paint, and gated to types, so a function
costs one kind test.

Layout is arithmetic (24px rows, 22px indent, orthogonal connectors computed
from the two): no ResizeObserver, same payload → same picture. The header's
`extends X` / `implemented by …` chips are suppressed while the tree is on
screen — two renderings of one relation in one column is how a reader ends up
trusting neither.

`TypeHierarchy` is exported from `@colbymchenry/codegraph-ui` and takes its data
as a prop, so a host holding a `WireSymbolPayload` renders it without a second
read.

scripts/check-ui-package.mjs

@@ -130,7 +130,7 @@ for (const [name, entry] of Object.entries(manifest.exports ?? {})) {
   }
 }
 
-// The five components the task names, plus the two seams they are useless
+// The exported screens, plus the two seams they are useless
 // without. Checked in the emitted JS, so a rename in index.ts that misses a
 // component fails here rather than in the Pro app.
 const entry = existsSync(join(DIST, 'index.js'))
@@ -138,6 +138,7 @@ const entry = existsSync(join(DIST, 'index.js'))
   : '';
 for (const name of [
   'SymbolView',
+  'TypeHierarchy',
   'FlowStrip',
   'ArchitectureMap',
   'TrailBar',