fix(overton): reframe verdict and migration as gateway domain

- Verdict now says 'window widened' (not 'did not shift') — centrist
  support surged for right-wing motions while staying flat for left-wing
- Migration reframed from 'one exception' to 'gateway domain' — where
  acceptance expanded most genuinely and right-wing parties learned
  frames they applied elsewhere
- Explorer Overton tab: added migration gateway section with pre/post
  metrics, full motion text (no truncation), 100-motion browser
- Explorer Kompas tab: updated Overton context to lead with the shift
- Explorer Trajectories tab: Dutch-language Overton annotation
- Synthesis, QMD, HTML report, STATUS.md all updated consistently

reports/overton_window/overton_report.html

@@ -538,6 +538,7 @@
   <div class="verdict">
     <ul>
       <li><strong>Overton shift confirmed for right-wing motions.</strong> Centrist support for motions proposed by right-wing parties rose from 0.384 to 0.620 after July 2024, while support for other party motions stayed flat. The shift is real and asymmetric.</li>
+      <li><strong>Migration is the gateway domain.</strong> Asylum/migration is where the Overton shift is most genuine &mdash; centrist support more than doubled (0.153 &rarr; 0.369) while material impact barely declined. Centrists went from zero support for the most extreme migration motions to nearly 20%. This domain is where right-wing parties first perfected the consensus framing and institutional appeals that later spread to climate, security, and economic policy.</li>
       <li><strong>Centrist tolerance increased at all gravity levels.</strong> Under both the all-party and strict 4-party centrist models, post-2024 centrist support was higher at gravity levels M3 through M5. The strict centrist core moved as well, not just the broader coalition.</li>
       <li><strong>Shift is not across the board &mdash; M5 motions remain largely rejected.</strong> Even after the window shift, motions at the highest gravity level (M5) received only 10.1% strict centrist support. Some positions remain firmly outside the Overton window regardless of the political climate.</li>
       <li><strong>Style and substance are only moderately correlated.</strong> With r = 0.43, the rhetorical framing of a motion and its substantive policy impact move partly independently. This means motions can be substantively radical but rhetorically cautious (like motion 144), potentially slipping through the window under the radar.</li>