feat(hh): ratatui TUI client — chat, live roster, themes

- Connect subcommand: SRP auth then a ratatui UI over tokio + crossterm.
- Async ws (tokio-tungstenite); reader task decrypts/parses frames into events.
- Panes: top bar (e2e + house N/cap), chat scrollback, roster (self marked ⛧),
  input box. Undecryptable frames surface as a system line, not a silent drop.
- Themes (vestments) via TOML --theme; default occult-monochrome + neon.
- Verified live in tmux: render, chat round-trip, roster, join/leave.
- Adds fernet python->rust interop regression test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hh/src/theme.rs

@@ -0,0 +1,48 @@
+//! Loadable colour/layout themes ("vestments"). Default is the churchofmalware
+//! occult-monochrome: black ground, white/grey ink, ⛧ accents. Override with a
+//! TOML file via `--theme <path>`.
+
+use ratatui::style::Color;
+use serde::Deserialize;
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(default)]
+pub struct Theme {
+    pub name: String,
+    pub border: Color,
+    pub title: Color,
+    pub accent: Color,
+    pub dim: Color,
+    pub me: Color,
+    pub other: Color,
+    pub system: Color,
+    pub input: Color,
+    pub roster_me: Color,
+    /// Width of the roster column.
+    pub roster_width: u16,
+}
+
+impl Default for Theme {
+    fn default() -> Self {
+        Self {
+            name: "crypt".into(),
+            border: Color::DarkGray,
+            title: Color::White,
+            accent: Color::White,
+            dim: Color::DarkGray,
+            me: Color::White,
+            other: Color::Gray,
+            system: Color::DarkGray,
+            input: Color::White,
+            roster_me: Color::White,
+            roster_width: 22,
+        }
+    }
+}
+
+impl Theme {
+    pub fn load(path: &str) -> anyhow::Result<Self> {
+        let s = std::fs::read_to_string(path)?;
+        Ok(toml::from_str(&s)?)
+    }
+}