E3: add community health files

The repository had no contributor-facing documentation or automation
config. Add the standard set:

- CHANGELOG.md (Keep a Changelog format, 0.1.0-0.1.4 plus Unreleased)
- CONTRIBUTING.md (build/test steps, change standards, PolyForm-NC note)
- SECURITY.md (private reporting, supported versions)
- CODE_OF_CONDUCT.md (Contributor Covenant 2.1)
- .github/ISSUE_TEMPLATE (bug report, feature request, config)
- .github/PULL_REQUEST_TEMPLATE.md
- .github/dependabot.yml (cargo, npm, pip, github-actions — the last
  keeps the D1 SHA pins current)
- .github/CODEOWNERS

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,39 @@
+---
+name: Bug report
+about: Report incorrect behaviour in Wickra
+title: "[bug] "
+labels: bug
+assignees: ""
+---
+
+## Description
+
+<!-- A clear description of what is wrong. -->
+
+## Reproduction
+
+<!-- Minimal code that reproduces the problem. -->
+
+```rust
+// or python / javascript
+```
+
+## Expected behaviour
+
+<!-- What you expected to happen, ideally with a reference value
+     (TA-Lib, pandas-ta, hand-computed). -->
+
+## Actual behaviour
+
+<!-- What happened instead. -->
+
+## Environment
+
+- Wickra version:
+- Language / binding: <!-- Rust crate / Python / Node / WASM -->
+- OS and architecture:
+- Rust / Python / Node version (if relevant):
+
+## Additional context
+
+<!-- Logs, screenshots, anything else. -->