Hub stage 1: apps across servers, read-only

hub/apps/matrix reads apps/list and each app's config on every server (the read
token first, the admin token once if a server refuses) and returns per app and server
the version, available update and a config hash, plus whether versions and configs
match and how many JSON leaf paths differ. Config texts never leave the hub. In hub
mode the Apps section has the server selector: All servers shows the matrix with
filters for differing versions, differing configs and updates; one server shows its
list without write actions. The dev mock takes --variant a|b with differing apps.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

hub/json-diff.ts

@@ -0,0 +1,38 @@
+/*
+A small structural diff of two JSON values: objects by key, arrays by index. A leaf that
+differs, a key present on one side only, and a change of type each give one entry.
+*/
+export interface JsonDifference {
+  path: string
+  a: unknown
+  b: unknown
+}
+
+const kind = (v: unknown): string => (v === null ? 'null' : Array.isArray(v) ? 'array' : typeof v)
+
+export function jsonDiff(a: unknown, b: unknown, path = ''): JsonDifference[] {
+  const ka = kind(a)
+  if (ka !== kind(b)) return [{ path, a, b }]
+  if (ka === 'array') {
+    const [xs, ys] = [a as unknown[], b as unknown[]]
+    const out: JsonDifference[] = []
+    for (let i = 0; i < Math.max(xs.length, ys.length); i++) {
+      const here = `${path}[${i}]`
+      if (i >= xs.length || i >= ys.length) out.push({ path: here, a: xs[i], b: ys[i] })
+      else out.push(...jsonDiff(xs[i], ys[i], here))
+    }
+    return out
+  }
+  if (ka === 'object') {
+    const [x, y] = [a as Record<string, unknown>, b as Record<string, unknown>]
+    const out: JsonDifference[] = []
+    for (const key of new Set([...Object.keys(x), ...Object.keys(y)])) {
+      const here = path === '' ? key : `${path}.${key}`
+      const [inX, inY] = [Object.hasOwn(x, key), Object.hasOwn(y, key)]
+      if (inX && inY) out.push(...jsonDiff(x[key], y[key], here))
+      else out.push({ path: here, a: x[key], b: y[key] })
+    }
+    return out
+  }
+  return a === b || (Number.isNaN(a) && Number.isNaN(b)) ? [] : [{ path, a, b }]
+}