feat(steps): rows read in the code's order; a hop written inside another call says so

- branch-guards callSiteInTree: a call's span and the call it is written inside the arguments of (`within`), stopping at a function or block boundary
- steps.ts: each step records the hop that first reached it (position, span, enclosing call — the fold's first hop out of the root, inherited down the fold); a row is ordered by that position, a hop inside another site's arguments before that site, and `WireStep.order` carries it; links carry `within`
- map-model: an `order` option — the row's initial order, sweeps over parents only, tie-broken by it; the Map and Screens tabs pass none and are unchanged
- viewer: rows laid out by `order`; `inside res.json(…)` in the panel rows and the tooltip
- tests: servers fixture (a token signed inside the reply's arguments: `within`, and the row `create · queue · mail · jwt.sign · 201`), model row order; spec §3.13, CHANGELOG

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01REFyW9hmNrxhwN5wxRoAkC

ui/src/lib/wire.ts

@@ -760,6 +760,8 @@ export interface WireStep {
   events?: string[];
   /** For a handler: what fires it. */
   trigger?: WireStepTrigger;
+  /** The step's place in its row, in the code's order (a hop written inside another site's arguments before that site). */
+  order?: number;
   /**
    * For a screen or an endpoint — also a `bridge` step that is an endpoint
    * reached across a tier: its path and the symbol that serves it.
@@ -795,6 +797,8 @@ export interface WireStepLink {
   when: string;
   /** How the last hop was established when it was not a plain call. */
   label: string;
+  /** The call the first hop is written inside the arguments of — `res.json` for a token signed while building the reply. */
+  within?: string;
   synthesized: boolean;
   uncertain: boolean;
   sites: WireStepSite[];