feat: Y2K dither theme, filter toolbars, chat bubble widget; fix alignment root causes

- theme rework (user request): white paper bg, brown ink, ordered-dither
  halftone textures, hard offset Y2K shadows, dithered masthead bands;
  dark theme matched; token test + DECISIONS updated
- fix: .card + .card stacking margin leaked into grid layouts, shifting
  every card except the first (the 'always the first item' reports)
- fix: CSP style-src 'self' silently dropped every inline style attribute
  (misaligned save button, stat values, editor attach button, bell badge);
  styles now allow inline, scripts remain strict per §12
- fix: [hidden] is now display:none !important so flex containers cannot
  defeat it (chat panel/footers)
- board + metrics filters live in boxed .toolbar rows with baseline-aligned
  controls; metric stat cards use a uniform .stat layout
- new-conversation dialog: fixed 440px width and 180px results list (no
  more resizing while searching), full-width result rows, picked people
  drop out of the list
- floating messages bubble bottom-right on all pages (except /messages):
  unread badge, mini panel with conversation list, thread view, quick
  composer, live WS updates; toasts moved up to clear it

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

web/templates/board.html

@@ -2,7 +2,7 @@
 <h1>Bounty Board</h1>
 <div class="error-box" id="error" role="alert"></div>
 
-<div class="row mt" id="board-filters">
+<div class="toolbar mt" id="board-filters">
   <div class="field">
     <label for="f-q">Search</label>
     <input type="search" id="f-q" placeholder="Search title or description… ( / )">
@@ -22,9 +22,7 @@
       <option value="bounty">Highest bounty</option>
     </select>
   </div>
-  <div class="field" style="flex:0;align-self:flex-end">
-    <button class="btn" id="f-save" title="Save current filters as default">Save</button>
-  </div>
+  <button class="btn" id="f-save" title="Save current filters as default">Save</button>
 </div>
 
 <div class="grid mt" id="board-grid"></div>