docs: rename repository from oil.nvim to canola.nvim

Problem: the fork shared the same name as upstream, making it difficult
to distinguish and discover independently.

Solution: rename the repository to canola.nvim — a type of oil, making
the lineage obvious while establishing a distinct identity. Update all
references in the README, rockspec, and issue templates.

.github/ISSUE_TEMPLATE/feature_request.yaml

@@ -9,7 +9,7 @@ body:
       options:
         - label:
             I have searched [existing
-            issues](https://github.com/barrettruth/oil.nvim/issues)
+            issues](https://github.com/barrettruth/canola.nvim/issues)
           required: true
 
   - type: textarea