🔧 Shared templates: convert the 15 emails to body fragments on the default layout #4133

What

Strip the shell, the copied CTA button, the sign-off and the no-reply footer out of the 15 config/templates/*.html files. Keep only the body, and use {{> button}} for the CTA.

Copy policy (intentional):

• Body text is preserved.
• The mail-specific line in the reset-password-email footer, "If you didn't make this request, you can ignore this email.", stays in its body.
• The shell is normalized: one signature from brand.signature, and the contact footer on every mail. The 4 org-* mails and referral-reward-earned gain the footer, and the "Support Team" variant (3 auth mails) becomes the brand signature.

Acceptance criteria

• Each template contains only its own body, with no hardcoded colors.
• Each mail's normalized text matches the baseline snapshot, except for the documented shell changes.
• Brand colors and a logo set in config show up in all 15 mails.

Tests

• Diff against the baseline snapshot, with an allow-list of the shell differences.
• One test that sets brand colors and logoUrl, then asserts them in all 15 rendered mails.

Depends on: layout and partials, and call sites (so appContact is always present for the new footers).

Needs: #4131