feat(hh): graceful shutdown, crypt default theme, neutralize branding, share-prep

- Graceful shutdown: Ctrl+C quits in chat (interrupts PTY while driving),
  RAII TermGuard + panic hook + SIGTERM/SIGHUP always restore the terminal
- Default theme is now "crypt" (neutral monochrome); theme sigil mirrored in
  chat/roster/help so the pentagram only renders under the "church" theme
- Neutralize inverted-pentagram branding across CLI, scripts, docs, and Cargo
  metadata (kept only in themes/church.toml + the render-time placeholder)
- Rewrite root README around hack-house; add bootstrap.sh, SECURITY.md,
  CODE_OF_CONDUCT.md, CHANGELOG.md, and issue/PR templates
- .gitignore cleanup; stop tracking .venv

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hh/direnv-autostart/.envrc

@@ -1,4 +1,4 @@
-# .envrc — cd into this directory to summon your hack-house ⛧
+# .envrc — cd into this directory to summon your hack-house
 #
 # Powered by direnv (https://direnv.net). Run ./setup.sh once to install direnv,
 # hook your shell, and `direnv allow` this file.
@@ -27,9 +27,9 @@ gen_pw() {
 # $HH_USER, then (inside tmux) switches your client into it. Guard against
 # stacking: if the session is already live, just point at it.
 if ! command -v tmux >/dev/null 2>&1; then
-    echo "⛧ install tmux to autostart your hack-house"
+    echo "install tmux to autostart your hack-house"
 elif tmux has-session -t "$SESSION" 2>/dev/null; then
-    echo "⛧ '$SESSION' already live — tmux attach -t $SESSION   (reveal its password in-app with /pw)"
+    echo "'$SESSION' already live — tmux attach -t $SESSION   (reveal its password in-app with /pw)"
 else
     PW="${PW:-$(gen_pw)}" "$HH_DIR/lets-hack.sh" "$HH_USER"
 fi