G2.3: Windy Git branding — and get it out of one host's disk into the repo

The front end was 100% stock Gitea: green teacup, "Gitea: Git with a cup of
tea", "A painless, self-hosted Git service". G2.3 was specified in the plan with
an acceptance test and never executed, and nothing enforced it.

Now: Windy Git name, wind-mark logo, brand-blue accent, and a landing page that
says what this actually is. Uses Gitea's SUPPORTED surface (custom templates +
public assets) so upstream upgrades keep arriving — no source modified (D-2/I-1).

Two traps this cost, both now documented and tested:

1. GITEA__DEFAULT__APP_NAME does not work. Gitea reads APP_NAME from the TOP
   LEVEL of app.ini; the env var created a literal [default] section that Gitea
   ignores, so the installer's stock APP_NAME kept winning while the config
   looked correct. The env-to-ini pass also APPENDED a second APP_NAME rather
   than replacing the first — a new variant of the documented G4A.3 trap.

2. Cloudflare caches /assets/* for 6h and no token in this stack can purge, so
   the new logo and CSS were invisible while being correct at origin. Brand
   assets now carry a VERSION IN THE FILENAME; bump it on every change.

Committed with an idempotent apply.sh, because applying it straight to Veron's
disk first was itself the config-drift trap this project documents: a rebuild
would have silently reverted to stock Gitea.

85 tests green.

Co-Authored-By: Claude (Fable 5) <noreply@anthropic.com>

deploy/branding/templates/custom/header.tmpl

@@ -0,0 +1,5 @@
+{{/* Windy Git brand layer.
+     The filename carries a version: Cloudflare caches /assets/* for 6h with no
+     purge token available to this stack, so editing a fixed filename leaves the
+     old bytes live for hours. Bump the suffix on every brand change. */}}
+<link rel="stylesheet" href="{{AssetUrlPrefix}}/css/theme-windy.v2.css">