feat(security): finish Windows firewall Public opt-in wiring + vuln-disclosure + doc cleanup

Firewall (the service.rs core landed in efb1ba2): scope the web-console rule
(TCP 47992) to Domain+Private by default with a `--allow-public-network` opt-in
that deletes-then-re-adds the rule, and add the installer "Allow connections on
Public networks" task (unchecked) forwarding the flag to `service install` and
`web setup`. Default is now trusted-networks-only; Public is explicit.

Vulnerability disclosure: SECURITY.md (report to security@punktfunk.com, scope,
SLAs, safe harbor), a Gitea issue-template contact link, a README security line,
and a Reporting section on the docs Security page.

Docs: the Security page now documents the Private/Domain firewall default (and
how to fix a misclassified-Public network / opt in); removed internal design-doc
and CLAUDE.md links from the user-facing docs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/ISSUE_TEMPLATE/config.yaml

@@ -0,0 +1,9 @@
+# Shown on the "new issue" chooser so security reports go to the private channel, not a public issue.
+blank_issues_enabled: true
+contact_links:
+  - name: 🔒 Report a security vulnerability
+    url: https://git.unom.io/unom/punktfunk/src/branch/main/SECURITY.md
+    about: >-
+      Found a security issue? Please report it privately by email to security@punktfunk.com — do not
+      open a public issue, so other users aren't exposed before a fix ships. See SECURITY.md for the
+      full policy.