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/jobs.html

@@ -17,7 +17,7 @@
 </form>
 </section>{% endfor %}</div>
 <h2>History</h2>
-{% if jobs.is_empty() %}<p class="muted text-sm">No jobs recorded yet.</p>{% else %}<div class="scroll-x tall"><table data-filter>
+{% if jobs.is_empty() %}<p class="muted text-sm">No jobs recorded yet.</p>{% else %}{% if jobs.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 data-filter>
 <thead><tr><th class="num">job</th><th>name</th><th>requested by</th><th>requested</th><th>started</th><th>finished</th><th class="num">duration</th><th>status</th><th>message</th><th class="num">run</th></tr></thead>
 <tbody>{% for job in jobs %}<tr>
 <td class="num"><a href="/dashboard/jobs/{{ job.id }}">{{ job.id }}</a></td>