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>

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,22 @@
+---
+name: Feature request
+about: Suggest an idea or enhancement
+title: "[feat] "
+labels: enhancement
+---
+
+## Problem / motivation
+What are you trying to do, and what's missing or painful today?
+
+## Proposed solution
+A clear and concise description of what you want to happen.
+
+## Alternatives considered
+Other approaches you thought about.
+
+## Security / privacy impact
+Does this touch encryption, the zero-knowledge server model, authentication, or
+sandbox permissions? If so, describe the impact.
+
+## Additional context
+Anything else — mockups, links, prior art.