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/themes/terminal-bus/static/css/terminal.css

@@ -0,0 +1,44 @@
+:root {
+  --bg: #0d1117;
+  --fg: #c9d1d9;
+  --green: #3fb950;
+  --amber: #d29922;
+  --dim: #8b949e;
+  --border: #30363d;
+}
+* { box-sizing: border-box; }
+body {
+  background: var(--bg);
+  color: var(--fg);
+  font-family: "JetBrains Mono", "Fira Code", ui-monospace, "SF Mono",
+    Menlo, monospace;
+  font-size: 15px;
+  line-height: 1.6;
+  max-width: 80ch;
+  margin: 0 auto;
+  padding: 1.5rem 1rem 4rem;
+}
+.banner { color: var(--green); font-size: 12px; line-height: 1.2;
+  overflow-x: auto; }
+.prompt { color: var(--green); font-weight: bold; }
+nav a, footer a { margin-right: 1.5ch; }
+a { color: var(--amber); text-decoration: none; }
+a:hover { text-decoration: underline; background: var(--amber);
+  color: var(--bg); }
+h1, h2, h3 { color: var(--green); font-size: 1.1em; margin-top: 2em; }
+h1 { font-size: 1.25em; }
+.date { color: var(--dim); margin-right: 2ch; }
+.post-list { list-style: none; padding: 0; }
+.post-list li { padding: 0.2em 0; }
+img { max-width: 100%; border: 1px solid var(--border); }
+pre, code { background: #161b22; }
+pre { padding: 1em; overflow-x: auto; border: 1px solid var(--border); }
+code { padding: 0.1em 0.4ch; }
+pre code { padding: 0; }
+blockquote { border-left: 3px solid var(--green); margin-left: 0;
+  padding-left: 1.5ch; color: var(--dim); }
+table { border-collapse: collapse; width: 100%; }
+th, td { border: 1px solid var(--border); padding: 0.3em 1ch;
+  text-align: left; }
+hr { border: 0; border-top: 1px dashed var(--border); }
+footer { margin-top: 4rem; color: var(--dim); font-size: 0.85em; }