feat: add Hugo blog with terminal-bus theme

Scaffold the bus.saillant.cc blog: Hugo site config, a hand-written
vendored theme (terminal-bus, zero deps), and the first post plus an
about page.

The theme is minimal on purpose: single baseof/home/page/section
layouts and one CSS file, styled as a terminal/hackerspace prompt
(green-on-dark, ASCII banner, monospace). No upstream theme pulled in,
per the no-blind-dependency policy.

Consumes journal entries later (Task 4); build output feeds deploy.sh
(Task 8). blog/public/ and blog/resources/ stay gitignored.

blog/hugo.toml

@@ -0,0 +1,15 @@
+baseURL = "https://bus.saillant.cc/"
+languageCode = "fr-fr"
+title = "bus.saillant.cc"
+theme = "terminal-bus"
+timeZone = "Europe/Paris"
+
+[params]
+  description = "Chantier d'un Irisbus Axer transformé en atelier/labo mobile — électronique, fab numérique, VASP."
+  prompt = "electron@bus"
+
+[permalinks]
+  posts = "/:year/:month/:slug/"
+
+[markup.goldmark.renderer]
+  unsafe = true