v0.8.5: WebUI process timeline, Gemini-style images, aligned layout

Process timeline: a run of consecutive thinking and tool calls is one
block that folds to a single line ("思考 4 次 · 工具 6 次"; while running
it shows the current action) and opens into a compact timeline, one row
per thought or call. Visible text, a note or the next prompt closes the
block; history and the live stream follow the same rule. show_thinking
now also applies while streaming instead of forcing thoughts open.

Layout: the avatar gutter and the flex-wrap that dropped it under long
answers are gone, so answer, process blocks, notes and composer share one
left edge. The text column and composer are both 720px (--content); the
rail and run panel grow with clamp() on wide screens. A rebuild after
each turn no longer replays every entrance animation, and the turn time
survives it. Message actions are icon buttons and only appear under text.

Images: a prompt's images sit above the bubble, right-aligned (one keeps
its shape, several are 152px rounded tiles) and open in a lightbox (Esc,
arrow keys). Images uploaded from the page show as thumbnails over the
composer and appear on the prompt as soon as it is sent.

Also: ?theme= is no longer overridden by app.js, the user bubble is
visible in the light theme, and the narrow top bar no longer wraps.

web/index.html

@@ -41,6 +41,10 @@
   <symbol id="i-lv4" viewBox="0 0 24 24"><path d="M4 18.5V13h2.6v5.5zM8.7 18.5V10h2.6v8.5zM13.4 18.5V6.8h2.6v11.7zM18.1 18.5V4h2.6v14.5z" class="f"/></symbol>
   <symbol id="i-file" viewBox="0 0 24 24"><path d="M13.5 3.5H7A2.5 2.5 0 0 0 4.5 6v12A2.5 2.5 0 0 0 7 20.5h10A2.5 2.5 0 0 0 19.5 18V9.5z"/><path d="M13.5 3.5v6h6"/></symbol>
   <symbol id="i-clock" viewBox="0 0 24 24"><circle cx="12" cy="12" r="8.5"/><path d="M12 7.2V12l3.2 2"/></symbol>
+  <symbol id="i-edit" viewBox="0 0 24 24"><path d="M14.8 5.2l4 4L9 19H5v-4z"/><path d="M12.6 7.4l4 4"/></symbol>
+  <symbol id="i-retry" viewBox="0 0 24 24"><path d="M4.5 12a7.5 7.5 0 0 1 13-5.1M19.5 12a7.5 7.5 0 0 1-13 5.1"/><path d="M17.8 3.6v3.6h-3.6M6.2 20.4v-3.6h3.6"/></symbol>
+  <symbol id="i-left" viewBox="0 0 24 24"><path d="M14.5 6l-6 6 6 6"/></symbol>
+  <symbol id="i-right" viewBox="0 0 24 24"><path d="M9.5 6l6 6-6 6"/></symbol>
   <symbol id="i-folder" viewBox="0 0 24 24"><path d="M3.5 6.5A1.5 1.5 0 0 1 5 5h4l2 2.5h8A1.5 1.5 0 0 1 20.5 9v9A1.5 1.5 0 0 1 19 19.5H5A1.5 1.5 0 0 1 3.5 18z"/></symbol>
 </svg>
 
@@ -216,6 +220,13 @@
 <div id="backdrop"></div>
 <div id="pop" class="pop" hidden></div>
 <div id="modal" hidden><div id="modal-box"></div></div>
+<div id="lightbox" hidden>
+  <img id="lb-img" alt="">
+  <button id="lb-close" class="lb-btn" title="关闭 (Esc)"><svg class="i"><use href="#i-close"/></svg></button>
+  <button id="lb-prev" class="lb-btn" title="上一张 (←)"><svg class="i"><use href="#i-left"/></svg></button>
+  <button id="lb-next" class="lb-btn" title="下一张 (→)"><svg class="i"><use href="#i-right"/></svg></button>
+  <span id="lb-count"></span>
+</div>
 <div id="toast" class="toast" role="status" aria-live="polite" hidden></div>
 <script>
 /* Layout is decided here, before app.js runs and before the first paint: the