feat: add mock investigation mode for UI development

- lib/mocks/confidence-engine/mock-client.js: self-contained ESM interceptor with 6 inline turn fixtures, no external deps or require() calls
- components/scenario-form.jsx: MOCK_ENABLED compile-time boolean, useMockGlobals() hook injects window.__MOCK_* globals at runtime, ternary dispatch to mockFetch
- .env.example: NEXT_PUBLIC_CONFIDENCE_ENGINE_MOCKS, MOCK_DELAY, MOCK_SCENARIO env vars
- docs/v0.7-ui-mock-mode.md: setup, scenarios (default/complete/error), architecture, safety rules, fixture schema

components/scenario-form.jsx

@@ -1,11 +1,27 @@
 "use client";
 
-import React from "react";
-import { useState, useRef, useEffect, useMemo } from "react";
+import React, { useEffect } from "react";
+import { useState, useRef, useMemo } from "react";
 import DiagnosticsView from "@/components/diagnostics-view";
 import GraphUpdateView from "@/components/graph-update-view";
 import SituationGraphView from "@/components/situation-graph-view";
 import ReasoningWorkspace, { LoadingOverlay } from "@/components/reasoning-workspace";
+import { mockFetch } from "@/lib/mocks/confidence-engine/mock-client";
+
+/* Compile-time env resolution — NEXT_PUBLIC_ vars are injected by Next.js at build */
+const MOCK_ENABLED = process.env.NEXT_PUBLIC_CONFIDENCE_ENGINE_MOCKS === "true";
+
+/* ── inject runtime globals for the mock client to read ──── */
+function useMockGlobals() {
+  useEffect(() => {
+    if (MOCK_ENABLED) {
+      var w = window;
+      w.__MOCK_ENABLED = true;
+      w.__MOCK_DELAY = process.env.NEXT_PUBLIC_CONFIDENCE_MOCK_DELAY || "normal";
+      w.__MOCK_SCENARIO = process.env.NEXT_PUBLIC_CONFIDENCE_ENGINE_MOCK_SCENARIO || "";
+    }
+  }, []);
+}
 
 const MAX_LENGTH = 10000;
 
@@ -191,6 +207,9 @@ export default function ScenarioForm() {
   const [lastSubmittedAnswer, setLastSubmittedAnswer] = useState("");
   const textareaRef = useRef(null);
 
+  /* Inject mock globals so the interceptor can read them at runtime */
+  useMockGlobals();
+
   const { elapsed: startElapsed, currentMessage: startMsg } = useLoadingStatus(
     INITIAL_MESSAGES,
     status === "loading"
@@ -214,7 +233,7 @@ export default function ScenarioForm() {
     setUpdateResult(null);
 
     try {
-      const res = await submitScenarioForStartCase(fetch, scenario);
+      const res = await submitScenarioForStartCase(MOCK_ENABLED ? mockFetch : fetch, scenario);
 
       const data = await res.json();
 
@@ -245,7 +264,7 @@ export default function ScenarioForm() {
     setUpdateError(null);
     setLastSubmittedAnswer(answer.trim());
 
-    const submission = await submitAnswerForUpdateCase(fetch, {
+    const submission = await submitAnswerForUpdateCase(MOCK_ENABLED ? mockFetch : fetch, {
       situationGraph: result?.situationGraph,
       previousQuestion: result?.selectedQuestion,
       answer,