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/bug_report.md

@@ -0,0 +1,33 @@
+---
+name: Bug report
+about: Report a problem so we can fix it
+title: "[bug] "
+labels: bug
+---
+
+**Do not report security vulnerabilities here.** See [SECURITY.md](../../SECURITY.md).
+
+## Describe the bug
+A clear and concise description of what went wrong.
+
+## To reproduce
+Steps to reproduce the behavior:
+1. Run '...'
+2. Type '...'
+3. See error
+
+## Expected behavior
+What you expected to happen instead.
+
+## Environment
+- Component: client (Rust) / server (Python) / scripts
+- OS:
+- Client version (`hack-house --version` or commit):
+- Sandbox backend (if relevant): local / docker / multipass
+- TLS mode: TLS / `--no-tls` / `--insecure`
+
+## Logs / output
+Paste relevant terminal output. **Redact the room password and any secrets.**
+
+## Additional context
+Anything else that might help.

.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.

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,26 @@
+## Summary
+What does this PR change, and why?
+
+## Related issues
+Closes #
+
+## Type of change
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Refactor / cleanup
+- [ ] Documentation
+- [ ] Tests
+
+## Checklist
+- [ ] `cargo build` and `cargo test` pass (client)
+- [ ] `cargo fmt` and `cargo clippy` are clean
+- [ ] `pytest` passes (server)
+- [ ] I did not commit secrets, `.venv`, or build artifacts
+- [ ] I updated docs / `CHANGELOG.md` where relevant
+
+## Security / privacy impact
+Does this affect encryption, the zero-knowledge server model, authentication,
+or sandbox permissions? If so, explain. If not, write "none".
+
+## How to test
+Steps for a reviewer to verify the change.