feat(site): 🫙 PCBJam landing revisions — branding, accuracy, positioning graphic

Founder review pass on the landing page, plus commit the landing-page
research/spec docs under features/lp.

Branding & assets:
- New PCBJam mark: convert the jam-jar image to favicon.svg (trimmed, rounded
  tile) and use it in the browser tab, header, and footer.
- Footer "Built by": flower mark + "Emergence Engineering" in white Oswald (the
  blog's title font, self-hosted via @fontsource) so it's legible on dark.
- Produce the positioning quadrant graphic (public/graphics) and drop the placeholder.

Copy / accuracy:
- Remove header GitHub link; point "Built by EE" + footer "About" to
  emergence-engineering.com; Built-by CTA -> mailto:contact@emergence-engineering.com.
- Replace the wrong testimonial with Greg Detre's real quote from EE's site.
- Drop blog icons from Multiplayer/Pillars/How-it-works; add "Coming soon" to
  live-cursors & pin-comment; drop the hard-coded Yjs mention.
- Rework monetization to free+local / paid cloud-sync; remove "no metered AI",
  "no per-seat toll", and the Flux price claim; soften the AI section.
- Reframe waitlist copy (incl. confirmation email) to newsletter + early access.

Fixes:
- Offset only #waitlist for the sticky header (scroll-margin-top); section
  anchors keep their original behavior.

Docs:
- Commit features/lp (copy spec, brand guide, competitive research) via force-add
  over the /features/ gitignore.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

site/src/sections/BuiltByEmergence.astro

@@ -44,11 +44,12 @@ const clients = [
   </div>
 
   <blockquote class="quote">
-    “For any new product, they’re my go-to dev house. They work fast and to super high quality.”
-    <cite>— Ben Whately</cite>
+    “They are incredibly smart, you can trust them, and they’re great to work with. I cannot
+    recommend them highly enough.”
+    <cite>— Greg Detre, Chief Data Scientist &amp; CTO</cite>
   </blockquote>
 
-  <a class="btn btn-ghost" href="/built-by-emergence">
+  <a class="btn btn-ghost" href="mailto:contact@emergence-engineering.com">
     Need something hard built? → Talk to the team
   </a>
 </SectionBand>