docs: adopt YOUR SMTP. YOUR RULES. tagline and hero line

Record canonical positioning in product.md and refresh the stamp, README,
and brand proof page now that inbound relay is in scope.

docs: keep SELF-HOSTED SMTP RELAY on the stamp

Revert the mark subtitle; tagline and hero line stay in product.md and README only.

docs/product.md

@@ -10,14 +10,25 @@ in [guide.md](guide.md); as-built technical detail in
 
 ## Purpose
 
-SelfPost is a self-hosted **outbound SMTP relay** with a web control panel,
-shipped as a single Docker image. It sends mail directly to the internet from
-your own IP with per-domain DKIM signing.
+SelfPost is a self-hosted **SMTP relay** with a web control panel, shipped as a
+single Docker image. It sends mail directly from your server with per-domain
+DKIM signing; an optional inbound relay forwards mail on port 25 without
+storing it.
 
 **Primary workflow:** configure the relay once (domains, DKIM, SASL
 applications), then point scripts and apps at the SMTP endpoint. SelfPost
 delivers as the configured sending domain.
 
+## Positioning
+
+| | Text |
+|---|---|
+| Stamp subtitle | SELF-HOSTED SMTP RELAY |
+| Tagline | YOUR SMTP. YOUR RULES. |
+| Hero line (README, GitHub) | Self-hosted SMTP relay with a web panel — one Docker image, no provider. |
+
+Brand assets and metrics: [docs/assets/selfpost-proof.html](assets/selfpost-proof.html).
+
 ---
 
 ## Deployment context (fixed assumptions)