feat(web): 2D directional dependency-graph renderer (TASK-1783) (#720)

* feat(web): 2D directional dependency-graph renderer (TASK-1783)

Add ItemGraph.svelte — a reusable, self-contained component that renders a
single item's dependency neighborhood as a 2D layered graph (parents above,
children below) via dagre layout + SVG.

- Lazy-imports @dagrejs/dagre so the layout lib stays out of the main
  bundle (confirmed split into its own chunk).
- Fetches via api.graph.getFocused; re-roots on an internal currentFocus so
  clicking a non-focus node navigates the chain, clicking the focus node (or
  Open ↗) opens it. Depth (1–5) selector + include-done toggle; breadcrumb
  back to the original root.
- Edge styling by type (hierarchy tethers, red directional blocks arrows,
  faint wiki-link dashes, muted others); collection-colored nodes with
  focus highlight + dimmed terminals; pan/zoom + fit-to-content; legend and
  a truncation notice.
- Reactivity follows CONVE-1688 (loadToken guard, no read+write of one rune
  in an effect) and CONVE-606 (data-load effect split from prop-sync).

Extract the collection palette into a shared $lib/graph/palette.ts and point
the 3D workspace graph at it too, so both views agree on collection colors.

Parent: PLAN-1780.

* fix(web): correct hierarchy layout direction + node border color-mix per Codex review (round 1)

- P1: 'parent'/'implements' edges are child→parent in the API, so feeding
  them to dagre as-is put children above parents under rankdir TB. Reverse
  those edges for layout ranking only; rendered edges keep true source→target
  so 'blocks' arrowheads still point correctly.
- P2: unfocused node border used a JS string literal with an un-interpolated
  {n.color}, yielding an invalid CSS color and a dropped stroke. Use a
  template literal so the collection tint actually applies.

Parent: PLAN-1780.

Author: xarmian

web/package-lock.json

@@ -36,6 +36,7 @@
 		}
 	},
 	"dependencies": {
+		"@dagrejs/dagre": "3.0.0",
 		"@tiptap/core": "^3.22.5",
 		"@tiptap/extension-bubble-menu": "^3.22.5",
 		"@tiptap/extension-code-block-lowlight": "^3.22.5",