targeted feedback: extend pin targets to flow edges, vega marks, mermaid, calltree

[ivanmkc]

v1 pin targets: pane, flow-node, component (props.id), checklist-item, markdown heading. Explicit non-goals deferred from the spec:

• flow edges — thin hit targets; verify React Flow edge DOM carries a resolvable data-id before enabling.
• vega-lite marks — no stable ids; would need scenegraph hit → encoding field/value capture.
• mermaid elements — rendered SVG has generated ids only.
• calltree nodes — tree rows have labels, not ids; a path-of-labels id scheme would work.

Everything else (wire format, composer, CLI, skill docs) is target-kind-agnostic — each of these is mostly a resolver branch in comment-target.ts plus a TARGET_KINDS entry server-side.

Context: docs/superpowers/specs/2026-07-03-targeted-feedback-design.md (non-goals), PR #220.