fix(collab): embed online badge in tab row instead of fixed overlay

The "N online" collab badge was position:fixed at top:8px, overlapping
the header login area. Move it into the tab bar slot (main shell) or
header-right section (standalone shells) so it flows inline with other
chrome elements.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/shell.ts

@@ -251,6 +251,7 @@ export function renderShell(opts: ShellOptions): string {
   </header>
   <div class="rstack-tab-row">
     <rstack-tab-bar space="${escapeAttr(spaceSlug)}" active="" view-mode="flat">
+      <rstack-collab-overlay module-id="${escapeAttr(moduleId)}" space="${escapeAttr(spaceSlug)}"></rstack-collab-overlay>
       <button class="rapp-info-btn" id="rapp-info-btn" title="About this rApp"><svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="10"/><line x1="12" y1="16" x2="12" y2="12"/><line x1="12" y1="8" x2="12.01" y2="8"/></svg></button>
     </rstack-tab-bar>
   </div>
@@ -271,7 +272,6 @@ export function renderShell(opts: ShellOptions): string {
     ${opts.tabs ? renderTabBar(opts.tabs, opts.activeTab, opts.tabBasePath || ((opts.isSubdomain ?? IS_PRODUCTION) ? `/${escapeAttr(moduleId)}` : `/${escapeAttr(spaceSlug)}/${escapeAttr(moduleId)}`)) : ''}
     ${body}
   </main>
-  <rstack-collab-overlay module-id="${escapeAttr(moduleId)}" space="${escapeAttr(spaceSlug)}"></rstack-collab-overlay>
 
   ${renderWelcomeOverlay()}
 
@@ -1409,7 +1409,9 @@ export function renderExternalAppShell(opts: ExternalAppShellOptions): string {
     </div>
   </header>
   <div class="rstack-tab-row">
-    <rstack-tab-bar space="${escapeAttr(spaceSlug)}" active="" view-mode="flat"></rstack-tab-bar>
+    <rstack-tab-bar space="${escapeAttr(spaceSlug)}" active="" view-mode="flat">
+      <rstack-collab-overlay module-id="${escapeAttr(moduleId)}" space="${escapeAttr(spaceSlug)}" mode="badge-only"></rstack-collab-overlay>
+    </rstack-tab-bar>
   </div>
   <div class="rspace-iframe-wrap">
     <div class="rspace-iframe-loading" id="iframe-loading">
@@ -1426,7 +1428,6 @@ export function renderExternalAppShell(opts: ExternalAppShellOptions): string {
     ></iframe>
     <a class="rspace-iframe-newtab" href="${escapeAttr(appUrl)}" target="_blank" rel="noopener">Open in new tab ↗</a>
   </div>
-  <rstack-collab-overlay module-id="${escapeAttr(moduleId)}" space="${escapeAttr(spaceSlug)}" mode="badge-only"></rstack-collab-overlay>
 
   <script type="module">
     import '/shell.js';
@@ -2012,11 +2013,11 @@ export function renderModuleLanding(opts: ModuleLandingOptions): string {
       <rstack-mi></rstack-mi>
     </div>
     <div class="rstack-header__right">
+      <rstack-collab-overlay module-id="${escapeAttr(mod.id)}" mode="badge-only"></rstack-collab-overlay>
       <rstack-identity></rstack-identity>
     </div>
   </header>
   ${bodyContent}
-  <rstack-collab-overlay module-id="${escapeAttr(mod.id)}" mode="badge-only"></rstack-collab-overlay>
   <script type="module">
     import '/shell.js';
     if ("serviceWorker" in navigator && location.hostname !== "localhost") {
@@ -2359,11 +2360,11 @@ export function renderSubPageInfo(opts: SubPageInfoOptions): string {
       <rstack-mi></rstack-mi>
     </div>
     <div class="rstack-header__right">
+      <rstack-collab-overlay module-id="${escapeAttr(mod.id)}" mode="badge-only"></rstack-collab-overlay>
       <rstack-identity></rstack-identity>
     </div>
   </header>
   ${bodyContent}
-  <rstack-collab-overlay module-id="${escapeAttr(mod.id)}" mode="badge-only"></rstack-collab-overlay>
   <script type="module">
     import '/shell.js';
     if ("serviceWorker" in navigator && location.hostname !== "localhost") {

shared/components/rstack-collab-overlay.ts

@@ -441,20 +441,13 @@ export class RStackCollabOverlay extends HTMLElement {
 
 const OVERLAY_CSS = `
 	:host {
-		display: block;
+		display: inline-flex;
-		position: fixed;
+		align-items: center;
-		top: 0;
-		left: 0;
-		width: 0;
-		height: 0;
-		z-index: 9999;
 		pointer-events: none;
+		position: relative;
 	}
 
 	.collab-badge {
-		position: fixed;
-		top: 8px;
-		right: 80px;
 		display: none;
 		align-items: center;
 		gap: 4px;
@@ -468,9 +461,9 @@ const OVERLAY_CSS = `
 		pointer-events: auto;
 		cursor: pointer;
 		user-select: none;
-		z-index: 10000;
 		border: 1px solid var(--rs-border, rgba(255,255,255,0.08));
 		transition: opacity 0.2s, border-color 0.2s;
+		white-space: nowrap;
 	}
 
 	.collab-badge:hover {