fix(api): close contract gaps found by post-merge adversarial audit

A 15-agent audit of the merged tree confirmed 9 envelope/contract bugs;
all fixed here, with live-server contract tests added:

Blockers (fresh-install quick start broken):
- session-ui.js runClaude/runShell unwrapped .data from the /api/cases/:name
  404 error envelope (which has no data key), so a not-yet-created case threw
  TypeError instead of triggering the auto-create fallback. Now '?.data ?? {}'.

Contract violations on the new stable surface:
- Unknown /api routes returned HTTP 404 with {success:true,...} (Fastify's
  default not-found payload was wrapped by the envelope hook). Added a
  setNotFoundHandler returning the standard error envelope for /api paths.
- POST /api/events/subscribe 400 body became {success:true,data:{error}};
  now createErrorResponse(INVALID_INPUT).
- POST /api/clipboard validation error lacked errorCode and shipped HTTP 200;
  now createErrorResponse(INVALID_INPUT) -> 400.
- POST /api/run catch path returned bare {success:false,sessionId,error}
  (HTTP 200, no errorCode); now OPERATION_FAILED envelope -> 422 with the
  dead session id in the message.
- DELETE tail-file/:streamId returned {success: closed}, colliding with the
  envelope discriminator; now returns {closed}.

Dead/regressed UI paths:
- Plan history modal could never open: route returned the bare history array
  under data while the frontend read data.data.history/currentVersion. Route
  now returns {history, currentVersion}; modal task count fixed to stats.total.
- Self-update error toast read j.error.message from the string-typed envelope
  error, always falling back to the generic message; now reads the string.

Cleanup:
- Removed the stale QuickStartResponse type (unreferenced; documented the
  pre-envelope shape and invited success-key collisions).

Tests: new test/http-contract.test.ts boots a real WebServer (port 3168) and
pins the envelope, /api/v1 alias, error statuses, and the /api 404 shape —
the route-test harness does not install the server-level hook, so these need
the live server. Updated file-routes/plan-routes/scheduled-runs tests to the
fixed shapes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/public/ralph-panel.js

@@ -1035,7 +1035,7 @@ Object.assign(CodemanApp.prototype, {
                    onclick="app.rollbackToPlanVersion(${item.version})">
                 <div>
                   <span class="plan-history-version">v${item.version}</span>
-                  <span class="plan-history-tasks">${item.taskCount || 0} tasks</span>
+                  <span class="plan-history-tasks">${item.stats?.total ?? 0} tasks</span>
                 </div>
                 <span class="plan-history-time">${this.formatRelativeTime(item.timestamp)}</span>
               </div>

src/web/public/session-ui.js

@@ -304,7 +304,7 @@ Object.assign(CodemanApp.prototype, {
     try {
       // Get case path first
       const caseRes = await fetch(`/api/cases/${caseName}`);
-      let caseData = (await caseRes.json()).data;
+      let caseData = (await caseRes.json())?.data ?? {};
 
       // Create the case if it doesn't exist
       if (!caseData.path) {
@@ -452,7 +452,7 @@ Object.assign(CodemanApp.prototype, {
     try {
       // Get the case path
       const caseRes = await fetch(`/api/cases/${caseName}`);
-      let caseData = (await caseRes.json()).data;
+      let caseData = (await caseRes.json())?.data ?? {};
 
       // Create the case if it doesn't exist
       if (!caseData.path) {

src/web/public/settings-ui.js

@@ -569,7 +569,7 @@ Object.assign(CodemanApp.prototype, {
     const res = await this._apiPost('/api/system/update', {});
     if (!res || !res.ok) {
       let msg = 'Failed to start the update.';
-      try { const j = await res.json(); if (j?.error?.message) msg = j.error.message; } catch {}
+      try { const j = await res.json(); if (typeof j?.error === 'string' && j.error) msg = j.error; } catch {}
       this._setUpdateProgress(`<span style="color:var(--danger,#e5534b)">${escapeHtml(msg)}</span>`);
       if (btn) { btn.disabled = false; btn.textContent = 'Update now'; }
       return;