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/messages.html

@@ -56,7 +56,7 @@
     <div class="field">
       <label for="nc-search">Participants</label>
       <input type="search" id="nc-search" placeholder="Search people…">
-      <div id="nc-results" class="stack" style="max-height:160px;overflow:auto"></div>
+      <div id="nc-results" role="listbox" aria-label="Search results"></div>
       <div id="nc-selected" class="mt"></div>
     </div>
     <div class="spread">