docs: add GitHub issue templates for bug reports and feature requests

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Bug report
+description: Report a bug or unexpected behavior in the viewer
+title: "[bug]: "
+labels: ["bug"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for taking the time to file a bug report. Please fill out the
+        fields below so the issue can be reproduced quickly.
+
+  - type: dropdown
+    id: container-tag
+    attributes:
+      label: Container tag
+      description: Which Lance Data Viewer container are you running?
+      options:
+        - "lancedb-0.29.2 (recommended)"
+        - "lancedb-0.24.3"
+        - "lancedb-0.16.0"
+        - "lancedb-0.5"
+        - "lancedb-0.3.4"
+        - "lancedb-0.3.1"
+        - "Built locally from source"
+        - "Other / unknown"
+    validations:
+      required: true
+
+  - type: input
+    id: host-os
+    attributes:
+      label: Host OS
+      description: "e.g. Ubuntu 22.04, macOS 14.4, Windows 11 with WSL2"
+      placeholder: "Ubuntu 22.04"
+    validations:
+      required: true
+
+  - type: input
+    id: lance-source
+    attributes:
+      label: Lance data source
+      description: "What wrote the Lance files you are viewing? (e.g. lancedb 0.29.2 via Python, an existing dataset, an Airflow pipeline)"
+      placeholder: "lancedb 0.29.2 via Python"
+    validations:
+      required: false
+
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What happened?
+      description: A clear description of the bug.
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected behavior
+      description: What did you expect to happen instead?
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduction
+    attributes:
+      label: Reproduction steps
+      description: Exact commands you ran, including the `docker run` or `docker compose` invocation if applicable.
+      render: shell
+    validations:
+      required: true
+
+  - type: textarea
+    id: logs
+    attributes:
+      label: Logs or error output
+      description: Paste any relevant logs from the container or browser console.
+      render: shell
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature request
+description: Suggest a new feature or enhancement
+title: "[feat]: "
+labels: ["enhancement"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for suggesting a feature. Before filing, please read the
+        design constraints in [CONTRIBUTING.md](https://github.com/lance-format/lance-data-viewer/blob/main/CONTRIBUTING.md).
+        Proposals that conflict with those constraints are unlikely to be
+        accepted without a strong justification.
+
+  - type: textarea
+    id: summary
+    attributes:
+      label: Summary
+      description: One or two sentences describing the feature.
+    validations:
+      required: true
+
+  - type: textarea
+    id: use-case
+    attributes:
+      label: Use case
+      description: What problem does this solve? Who benefits and how?
+    validations:
+      required: true
+
+  - type: textarea
+    id: approach
+    attributes:
+      label: Proposed approach
+      description: If you have an implementation sketch, share it here. Optional.
+    validations:
+      required: false
+
+  - type: checkboxes
+    id: constraints
+    attributes:
+      label: Design constraint check
+      description: |
+        Confirm the proposal is compatible with the project's load-bearing
+        design constraints:
+        - Vanilla JS with no build step
+        - GET-only, stateless API
+        - No metadata database
+        - No in-app authentication
+        - Read-only access
+      options:
+        - label: "I have read CONTRIBUTING.md and this proposal does not conflict with the load-bearing design constraints."
+          required: true