MVP M5 (in-memory): bidirectional sync via ModelOp + applyOps + ModelStore

Both canvases now share a canonical SysMLModel through React context.
Renames in the diagram inspector ripple to every chip in the narrative
referencing the same refId, and double-clicking a chip emits an update op
that re-renders the diagram block. Validation re-runs on every successful
apply. State is in-memory; M5.9 adds Postgres persistence.

apps/web/lib/sync (new)
- ops.ts: ModelOp alphabet (18 op kinds across block / property /
  association / constraint / requirement / relation, add/update/remove for
  each). tempId() helper + per-kind constructors.
- applyOps.ts: pure (model, ops) → { model, idMapping, errors, applied }
  reducer. Atomic per batch. Cascades on remove-block (drops incident
  associations + constraint applies-to + requirement satisfiers). tempId
  resolution rewrites to canonical ids on duplicate-id collision.
- ModelStore.tsx: React provider exposing { model, apply, issues,
  issuesByElement }. Validation memoized on every model change.

Editor refactor
- EditorShell wraps in ModelStoreProvider. Initial model derived from
  fixture (+ optional ?break= corruptions). Validation now lives in the
  store, not duplicated here.
- LeftRail consumes useModel(): Model section lists real blocks +
  constraints (sorted by kind), Requirements section lists real
  requirements with traced/untraced status from r.relations.

Diagram refactor (the tricky piece)
- React Flow now owns ephemeral state via useNodesState / useEdgesState.
  Positions, drag-in-progress, selection are all RF-internal.
- Model → RF: a useEffect runs on model change, applies targeted setNodes
  updates only for elements whose semantic data (label, kind, properties)
  changed. Object identity preserved for unchanged nodes — fixes the
  "re-render storm on drag" + RF measurement-cache loss.
- RF → Model: onNodesChange / onEdgesChange / onConnect / onDrop emit
  ops via useApply(). Constraint-applies edges decompose into
  updateConstraint ops. deleteKeyCode={[Backspace, Delete]}.
- onNodesChange now handles type:'remove' too (was missing — that's why
  selecting a block + Del removed only the edges, leaving the block).

Chip refactor
- ChipView resolves displayed label from useModel() via refId lookup
  (block / requirement / association / property). Double-click chip →
  inline rename input → emit update-{block,requirement,association} op.
  All other chips with the same refId update on the next render.
- Slash-menu inserted chips have refId=null and skip the rename
  affordance (until M6 wires real model element resolution).

Removed obsolete components/diagram-canvas/fixtureToFlow.ts; replaced
with modelToFlow.ts. Bumped CSS for the chip-rename input.

apps/web/app/editor/[projectId]/page.tsx

@@ -1,16 +1,10 @@
-import { Suspense } from "react";
 import { EditorShell } from "../../../components/editor/EditorShell";
 import { aristotleFixture } from "../../../lib/fixtures/aristotle";
 
 // M1: every projectId resolves to the Aristotle fixture.
 // M4–M5 wire this to a real database lookup.
-//
-// Suspense boundary required because EditorShell uses useSearchParams (for
-// the M4 ?break=... demo of validation rules).
+// (EditorShell wraps itself in Suspense for useSearchParams; no boundary
+// needed at this level.)
 export default async function EditorPage(_props: { params: Promise<{ projectId: string }> }) {
-  return (
-    <Suspense fallback={null}>
-      <EditorShell data={aristotleFixture} />
-    </Suspense>
-  );
+  return <EditorShell data={aristotleFixture} />;
 }