chore(repo): fix license detection and add github workflows

LICENSE now starts with the EUPL-1.2 standard header so github-linguist
detects the licence correctly in the repo header. The dual-copyright
block (upstream ChatTwo authors plus Hellion Online Media) moves into a
new COPYRIGHT file referenced from the README. NOTICE.md and
UPSTREAM_SYNC.md stay as-is.

New files under .github:

- workflows/build.yml: validates every push to main and every PR
  against the current Dalamud staging branch on a Windows runner
- workflows/release.yml: builds Release on every v* tag, locates the
  DalamudPackager latest.zip and attaches it to the matching GitHub
  Release via softprops/action-gh-release
- dependabot.yml: weekly NuGet sweeps and monthly GitHub Actions
  sweeps with conventional-commit prefixes, grouped patch and minor
  PRs to cut review noise
- ISSUE_TEMPLATE/bug_report.yml + feature_request.yml + config.yml:
  structured intake that pushes security reports through the private
  advisory flow and routes upstream-only issues to ChatTwo
- SECURITY.md: documents the vulnerability reporting channels, scope,
  and target disclosure window

The release workflow replaces the previous manual upload step. Tag a
release and the ZIP shows up on the release page automatically.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,14 @@
+blank_issues_enabled: false
+
+contact_links:
+  - name: Security vulnerability
+    url: https://github.com/JonKazama-Hellion/HellionChat/security/advisories/new
+    about: Do not open a public issue for security problems. Use the private advisory instead.
+
+  - name: Upstream Chat 2 issue
+    url: https://github.com/Infiziert90/ChatTwo/issues
+    about: If the issue exists in upstream Chat 2 too, please report it there so the original maintainers see it as well.
+
+  - name: Discord
+    url: https://discord.com/users/j.j_kazama
+    about: Quick questions, casual feedback. Bug reports still go through the issue tracker for tracking.