Draw every flow as one graph, merged on what it talks to

A node type can now say which outside thing its parameters point at, and
nodes sharing one — a broker topic, a URL, a bucket — are drawn as a single
neuron on a new /brain canvas. That makes the wiring which runs between
flows through a broker visible for the first time; no single flow's canvas
can show it. The key is read off stored parameters, so a credential
reference never reaches an id.

Layout is a d3 force simulation settled once and then frozen, lit by the
socket the editor already listens to: a neuron pulses when any node behind
it publishes, and its connections light as values pass.

Fixes the message pulse while here: interpolating the stroke against the
edge's `color-mix()` resting colour went through oklab and left the gamut,
which turned every pulse on both canvases fluorescent yellow.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017MeiWk3Yq12n2pTvnQWYvt

bun.lock

@@ -36,6 +36,7 @@
         "class-variance-authority": "^0.7.1",
         "clsx": "^2.1.1",
         "cmdk": "^1.1.1",
+        "d3-force": "^3.0.0",
         "form-data": "4.0.5",
         "lucide-react": "^0.562.0",
         "monaco-editor": "^0.56.0",
@@ -60,6 +61,7 @@
         "@playwright/test": "1.58.0",
         "@tanstack/router-devtools": "^1.142.11",
         "@tanstack/router-plugin": "^1.140.0",
+        "@types/d3-force": "^3.0.10",
         "@types/node": "^25.0.10",
         "@types/react": "^19.2.7",
         "@types/react-dom": "^19.2.3",
@@ -482,6 +484,8 @@
 
     "@types/d3-drag": ["@types/d3-drag@3.0.7", "", { "dependencies": { "@types/d3-selection": "*" } }, "sha512-HE3jVKlzU9AaMazNufooRJ5ZpWmLIoc90A37WU2JMmeq28w1FQqCZswHZ3xR+SuxYftzHq6WU6KJHvqxKzTxxQ=="],
 
+    "@types/d3-force": ["@types/d3-force@3.0.10", "", {}, "sha512-ZYeSaCF3p73RdOKcjj+swRlZfnYpK1EbaDiYICEEp5Q6sUiqFaFQ9qgoshp5CzIyyb/yD09kD9o2zEltCexlgw=="],
+
     "@types/d3-interpolate": ["@types/d3-interpolate@3.0.4", "", { "dependencies": { "@types/d3-color": "*" } }, "sha512-mgLPETlrpVV1YRJIglr4Ez47g7Yxjl1lj7YKsiMCb27VJH9W8NVM6Bb9d8kkpG/uAQS5AmbA48q2IAolKKo1MA=="],
 
     "@types/d3-selection": ["@types/d3-selection@3.0.11", "", {}, "sha512-bhAXu23DJWsrI45xafYpkQ4NtcKMwWnAC/vKrd2l+nxMFuvOT3XMYTIj2opv8vq8AO5Yh7Qac/nSeP/3zjTK0w=="],
@@ -582,8 +586,12 @@
 
     "d3-ease": ["d3-ease@3.0.1", "", {}, "sha512-wR/XK3D3XcLIZwpbvQwQ5fK+8Ykds1ip7A2Txe0yxncXSdq1L9skcG7blcedkOX+ZcgxGAmLX1FrRGbADwzi0w=="],
 
+    "d3-force": ["d3-force@3.0.0", "", { "dependencies": { "d3-dispatch": "1 - 3", "d3-quadtree": "1 - 3", "d3-timer": "1 - 3" } }, "sha512-zxV/SsA+U4yte8051P4ECydjD/S+qeYtnaIyAs9tgHCqfguma/aAQDjo85A9Z6EKhBirHRJHXIgJUlffT4wdLg=="],
+
     "d3-interpolate": ["d3-interpolate@3.0.1", "", { "dependencies": { "d3-color": "1 - 3" } }, "sha512-3bYs1rOD33uo8aqJfKP3JWPAibgw8Zm2+L9vBKEHJ2Rg+viTR7o5Mmv5mZcieN+FRYaAOWX5SJATX6k1PWz72g=="],
 
+    "d3-quadtree": ["d3-quadtree@3.0.1", "", {}, "sha512-04xDrxQTDTCFwP5H6hRhsRcb9xxv2RzkcsygFzmkSIOJy3PeRJP7sNk3VRIbKXcog561P9oU0/rVH6vDROAgUw=="],
+
     "d3-selection": ["d3-selection@3.0.0", "", {}, "sha512-fmTRWbNMmsmWq6xJV8D19U/gw/bwrHfNXxrIN+HfZgnzqTHp9jOmKMhsTUjXOJnZOdZY9Q28y4yebKzqDKlxlQ=="],
 
     "d3-timer": ["d3-timer@3.0.1", "", {}, "sha512-ndfJ/JxxMd3nw31uyKoY2naivF+r29V+Lc0svZxe1JvvIRmi8hUsrMvdOwgS1o6uBHmiz91geQ0ylPP0aj1VUA=="],