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/runs.html

@@ -7,7 +7,7 @@
 <label>Status <select name="status"><option value="">any</option>{% for name in statuses %}<option value="{{ name }}"{% if status == *name %} selected{% endif %}>{{ name }}</option>{% endfor %}</select></label>
 <div class="filter-actions"><button class="btn" type="submit">Filter</button>{% if !status.is_empty() %}<a class="btn-quiet" href="/dashboard/runs">Reset</a>{% endif %}</div>
 </form>
-<div class="scroll-x tall"><table data-filter>
+{% if runs.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>run</th><th>date</th><th>status</th><th>started</th><th>duration</th><th>considered → eligible → triaged → assessed → shortlisted → selected</th><th>cost</th><th class="num">total</th><th class="num">warnings</th></tr></thead>
 <tbody>{% for run in runs %}<tr>
 <td class="num"><a href="/dashboard/runs/{{ run.id }}">{{ run.id }}</a></td>