feat: add community infrastructure and update server setup

- releases/manifest.json: Seed release manifest for update server
- update.rs: Make UPDATE_MANIFEST_URL configurable via ARCHIPELAGO_UPDATE_URL env var
- CONTRIBUTING.md: Comprehensive contribution guidelines covering code style,
  PR process, testing, security disclosure, and app submission
- .github/ISSUE_TEMPLATE/: Bug report, feature request, and app submission
  issue templates with structured forms
- .github/pull_request_template.md: PR template with checklist

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,44 @@
+name: Feature Request
+description: Suggest a new feature or improvement
+title: "[Feature]: "
+labels: ["enhancement"]
+body:
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem
+      description: What problem does this solve?
+      placeholder: I'm always frustrated when...
+    validations:
+      required: true
+
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed Solution
+      description: How should this work?
+    validations:
+      required: true
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives Considered
+      description: What other approaches did you consider?
+
+  - type: dropdown
+    id: area
+    attributes:
+      label: Area
+      options:
+        - Web UI
+        - Backend / API
+        - App Management
+        - Networking
+        - Security
+        - Web5 / Identity
+        - ISO / Installation
+        - Documentation
+        - Other
+    validations:
+      required: true