docs: Add RFC discussion template; fix table header styling

- Add .github/DISCUSSION_TEMPLATE/rfc.yml for enhancement proposals
- Fix table header alignment (center instead of right)
- Fix excessive padding in table headers by removing p tag margins

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko

.github/DISCUSSION_TEMPLATE/rfc.yml

@@ -0,0 +1,107 @@
+title: "[RFC] "
+labels:
+  - rfc
+  - "status: proposed"
+body:
+  - type: markdown
+    attributes:
+      value: |
+        ## DataJoint Enhancement Proposal
+
+        Use this template to propose changes to DataJoint specifications, APIs, or documentation structure.
+
+        **Before submitting:**
+        - Search existing discussions to avoid duplicates
+        - Consider starting with an informal discussion in the Ideas category first
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Summary
+      description: A brief, one-paragraph explanation of the proposal.
+      placeholder: This proposal adds/changes/removes...
+    validations:
+      required: true
+
+  - type: textarea
+    id: motivation
+    attributes:
+      label: Motivation
+      description: |
+        Why is this change needed? What problem does it solve?
+        Include concrete use cases and examples where possible.
+      placeholder: |
+        Currently, users need to...
+        This causes problems when...
+        With this change, users could...
+    validations:
+      required: true
+
+  - type: textarea
+    id: design
+    attributes:
+      label: Proposed Design
+      description: |
+        Detailed explanation of the proposed solution.
+        Include code examples, API signatures, or schema definitions as appropriate.
+      placeholder: |
+        ## API Changes
+        ```python
+        # Example usage
+        ```
+
+        ## Behavior
+        - When X happens, Y should occur
+        - Error handling: ...
+    validations:
+      required: true
+
+  - type: textarea
+    id: alternatives
+    attributes:
+      label: Alternatives Considered
+      description: What other approaches were considered and why were they not chosen?
+      placeholder: |
+        1. Alternative A: ...
+           Rejected because: ...
+
+        2. Alternative B: ...
+           Rejected because: ...
+
+  - type: textarea
+    id: compatibility
+    attributes:
+      label: Backwards Compatibility
+      description: |
+        How does this affect existing users?
+        - Breaking changes?
+        - Migration path?
+        - Deprecation timeline?
+      placeholder: |
+        This change is/is not backwards compatible.
+
+        Migration path:
+        1. ...
+
+  - type: textarea
+    id: implementation
+    attributes:
+      label: Implementation Notes
+      description: |
+        Optional: Technical details, affected files, estimated scope.
+        Prototyping in parallel with RFC discussion is encouraged.
+      placeholder: |
+        Affected components:
+        - datajoint-python/src/datajoint/...
+
+        Estimated scope: small/medium/large
+
+  - type: checkboxes
+    id: checklist
+    attributes:
+      label: Checklist
+      options:
+        - label: I have searched existing discussions and issues for duplicates
+          required: true
+        - label: I have considered backwards compatibility
+          required: true

src/datajoint/preview.py

@@ -122,7 +122,10 @@ def get_html_display_value(tup, name, idx):
         }
         .Table th{
             background: #A0A0A0; color: #ffffff; padding:2px 4px; border:#f0e0e0 1px solid;
-            font-weight: normal; font-family: monospace; font-size: 75%;
+            font-weight: normal; font-family: monospace; font-size: 75%; text-align: center;
+        }
+        .Table th p{
+            margin: 0;
         }
         .Table td{
             padding:2px 4px; border:#f0e0e0 1px solid; font-size: 75%;
@@ -168,7 +171,7 @@ def get_html_display_value(tup, name, idx):
         /* Dark mode support */
         @media (prefers-color-scheme: dark) {
             .Table th{
-                background: #4a4a4a; color: #ffffff; border:#555555 1px solid;
+                background: #4a4a4a; color: #ffffff; border:#555555 1px solid; text-align: center;
             }
             .Table td{
                 border:#555555 1px solid;
@@ -203,7 +206,7 @@ def get_html_display_value(tup, name, idx):
     {title}
         <div style="max-height:1000px;max-width:1500px;overflow:auto;">
         <table border="1" class="Table">
-            <thead> <tr style="text-align: right;"> <th> {head} </th> </tr> </thead>
+            <thead> <tr> <th> {head} </th> </tr> </thead>
             <tbody> <tr> {body} </tr> </tbody>
         </table>
         {ellipsis}