release: 1.9.3: Panel-redesign prep: mockups, routes, design contract (docs only)

Panel-redesign prep, docs only: stage 1-2 mockups on all 33 screens, the accepted header/type-scale/contrast corrections, the account e-mail and inbound-delegation decisions, and the routes/quarantine/preflight roadmap screens. Nothing in `internal/web` changes; the design stays `candidate` (3/21) until the redesign itself ships as `2.0.0`.
Added:
  - Panel redesign, account e-mail and notifications: a user's e-mail is its own
  - Panel redesign, contrast: a sweep of every text node against its real ground
  - Panel redesign, header (owner's choice: variant A, with the perforation on a
  - Panel redesign, type scale: about 40 % of the panel's text measured under
  - Panel redesign, header comparison sheet
  … (8 more in CHANGELOG)

Full detail: CHANGELOG.md (1.9.3).

README.md

@@ -112,7 +112,7 @@ docker run --rm -d --name selfpost-try \
   -e SELFPOST_HOSTNAME=mail.local.test \
   -e PANEL_COOKIE_SECURE=false \
   -v selfpost-try-data:/data \
-  ghcr.io/mixeme/selfpost:1.9.2
+  ghcr.io/mixeme/selfpost:1.9.3
 ```
 
 **Get the setup URL** (pick one):