feat: email design & copy upgrade for all 9 transactional emails

Redesigned _email_wrap(): lowercase wordmark header matching website,
3px blue accent border, preheader text support, HR separators.
_email_button() now full-width block for mobile tap targets.

Rewrote copy: improved subject lines, urgency cues, quick-start links
in welcome, styled project recap in quote verify, heat badges on lead
forward, "what happens next" in lead matched, secondary CTAs.

~30 new/updated translation keys in both EN and DE.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -38,6 +38,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   translated footer; ~70 new translation keys (EN + DE); all task payloads now
   carry `lang` from request context at enqueue time; payloads without `lang`
   gracefully default to English
+- **Email design & copy upgrade** — redesigned `_email_wrap()`: replaced monogram
+  header with lowercase wordmark matching website, added 3px blue accent border,
+  preheader text support (hidden preview in email clients), HR separators between
+  heading and body; `_email_button()` now full-width block for mobile tap targets;
+  rewrote copy for all 9 emails with improved subject lines, urgency cues,
+  quick-start links in welcome email, styled project recap cards in quote
+  verification, heat badges on lead forward emails, "what happens next" section
+  in lead matched notifications, and secondary CTAs; ~30 new/updated translation
+  keys in both EN and DE
 
 ### Changed
 - **Resend audiences restructured** — replaced dynamic `waitlist-{blueprint}`