feat: unified header across all pages (Notion-inspired breadcrumb + actions)

Created a shared _header.html template with:
- Hamburger button (toggle sidebar)
- Breadcrumb navigation with clickable segments and separators
- Page icon + title display
- Right-side action buttons (configurable per page)
- Dropdown panel CSS for More/New menus

Updated all pages to use the unified header:
- workspaces.html: Home / Workspaces + login/settings
- workspace.html: Workspace — Projects + login/settings
- local_workspace.html: workspace name
- gitea_workspace.html: Home / owner/repo + New/Upload/Refresh/Settings
- page_editor.html: title + Edited/Share/Copy/Favorite/More dropdown
- settings.html: Settings

Added CSS for breadcrumb, dropdown panel components.

app/templates/page_editor.html

@@ -1,13 +1,9 @@
 {% extends "base.html" %} {% block page_icon %}📄{% endblock %} {% block
 page_title %}{{ page.title }}{% endblock %} {% block topbar %}
-<header class="topbar" style="background:var(--bg-primary);">
-  <button class="hamburger-btn" @click="mobileSidebarOpen = true; sidebarCollapsed = false;" title="Menu">
-    <svg width="22" height="22" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><line x1="3" y1="6" x2="21" y2="6"/><line x1="3" y1="12" x2="21" y2="12"/><line x1="3" y1="18" x2="21" y2="18"/></svg>
-  </button>
-  <div class="topbar-left">
-    <span class="breadcrumb" style="color:rgba(255,255,255,.5);font-size:13px">{{ page.title }}</span>
-  </div>
-</header>
+{% set page_icon = "📄" %}
+{% set page_title = page.title %}
+{% set right_actions = '<span class="topbar-edited">Edited just now</span><button class="topbar-btn share-btn" @click="shareOpen = !shareOpen">🔒 Share ▾</button><button class="topbar-btn" @click="copyPageLink" title="Copy link">🔗</button><button class="topbar-btn star-btn" @click="toggleFavorite">⭐</button><button class="topbar-btn" @click="moreOpen = !moreOpen" style="position:relative">⋯<div class="dropdown-panel" :class="{ visible: moreOpen }" @click.outside="moreOpen=false" style="top:100%;right:0;left:auto;min-width:200px"><div class="dropdown-option" @click="moreOpen=false">📋 Duplicate</div><div class="dropdown-option" @click="moreOpen=false">🗑 Move to Trash</div><div class="dropdown-option" @click="moreOpen=false">🔗 Copy link</div><div class="dropdown-option" @click="moreOpen=false">📤 Export</div></div></button>' %}
+{% include '_header.html' %}
 {% endblock %} {% block content %}
 <div class="page-editor-wrapper" x-data="editorState()">
     <!-- ═══════════ Top Action Bar ═══════════ -->