feat: add issue and PR templates

Add structured issue templates for bug reports and feature requests,
with dropdown menus for channel, LLM provider, Python version, and OS.
Redirect questions to Discussions. Add PR template with checklist.

Ref: https://github.com/HKUDS/nanobot/discussions/3284

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -0,0 +1,55 @@
+name: Feature Request
+description: Suggest a new feature or enhancement
+labels: ["enhancement"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for suggesting a feature! Please describe your idea clearly.
+
+  - type: textarea
+    id: problem
+    attributes:
+      label: Problem / Motivation
+      description: What problem does this feature solve? What are you trying to accomplish?
+      placeholder: I'm always frustrated when ...
+    validations:
+      required: true
+
+  - type: textarea
+    id: solution
+    attributes:
+      label: Proposed Solution
+      description: How would you like this to work?
+    validations:
+      required: true
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives Considered
+      description: What other approaches have you considered?
+
+  - type: dropdown
+    id: component
+    attributes:
+      label: Related Component
+      description: Which part of nanobot does this relate to?
+      options:
+        - Channel (WeChat, Feishu, Telegram, etc.)
+        - LLM Provider
+        - Agent / Prompts
+        - Skills / Plugins
+        - Configuration
+        - CLI
+        - API Server
+        - Documentation
+        - Other
+    validations:
+      required: true
+
+  - type: textarea
+    id: additional
+    attributes:
+      label: Additional Context
+      description: Any other context, examples from other projects, screenshots, etc.