Remove everything that can change after first paint

Firefox users saw a flash on the first navigation after an idle spell, and
Chrome occasionally flashed white. Nothing in the network path explained it
(assets are immutable, the stylesheet is render-blocking, a cold Firefox
load paints fully styled), so this removes every remaining way a page could
look different between its first paint and its final state:

- Both Newsreader faces are embedded in the served stylesheet as data: URIs
  (CSP gains `font-src 'self' data:`; the preloads go away). A font fetched
  by URL is applied after first paint whenever the browser has to bring it
  back from disk, which is exactly the "first click after a while" case.
- The cross-document view transition is gone; the operator wants snappy.
- A color-scheme meta, kept in step with the saved theme, so the canvas the
  browser paints before the stylesheet is the right shade.
- The theme toggle's icon and label are chosen by CSS from html[data-theme]
  (set pre-paint by theme.js) instead of being rewritten by app.js.
- Dashboard table filters are rendered by the templates (shown under
  `.has-js`) rather than inserted by app.js, so tables no longer jump.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MD4VWGq6mGcd8Bg67qyx9k

src/web/templates/dashboard/articles.html

@@ -17,7 +17,7 @@
 <div class="filter-actions"><button class="btn" type="submit">Apply</button> <a class="btn-quiet" href="/dashboard/articles">Reset</a></div>
 </form>
 {% include "dashboard/_pager.html" %}
-<div class="scroll-x tall"><table class="articles" data-filter>
+{% if articles.len() > 1 %}<input type="search" class="table-filter" placeholder="Filter rows on this page" aria-label="Filter rows on this page" data-table-filter>{% endif %}<div class="scroll-x tall"><table class="articles" data-filter>
 <thead><tr><th>first seen</th><th>title</th><th>feed</th><th class="num">words</th><th>last stage</th><th>reason</th><th class="num">utility</th><th class="num">triage</th><th class="num">quality</th><th class="num">fit</th><th>rating</th><th>published</th></tr></thead>
 <tbody>{% for article in articles %}<tr>
 <td class="cell-tight text-muted">{{ article.first_seen }}</td>