feat: named case-result load combinations with full GUI support

Snapshots the current development tree, headlined by proper load
combinations (user request): a reusable LoadCombination entity of
weighted completed static-case results (e.g. 1.2xDead + 1.6xLive).

- core: LoadCombination/LoadCombinationItem entities, Project
  integration (lookup, unique ids, reference validation)
- services: combinations.py (linear superposition + envelope),
  exported via services __init__
- commands: undoable Add/Delete/Update for combinations
- GUI: Load Combinations manager dialog, Run-dialog evaluation,
  envelope display in Results panel, Combinations tab in Table dock
- tests: unit coverage (validation, math, error paths) + integration
  superposition check vs a single factored run

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -0,0 +1,56 @@
+name: Bug report
+description: Report a defect in OTKO
+labels: ["bug"]
+body:
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What happened?
+      description: A clear and concise description of the bug.
+    validations:
+      required: true
+  - type: textarea
+    id: reproduce
+    attributes:
+      label: Steps to reproduce
+      placeholder: |
+        1. Open a new project
+        2. Click 'Draw Frame'
+        3. ...
+    validations:
+      required: true
+  - type: textarea
+    id: expected
+    attributes:
+      label: Expected behavior
+    validations:
+      required: true
+  - type: input
+    id: version
+    attributes:
+      label: OTKO version
+      placeholder: 0.0.1
+    validations:
+      required: true
+  - type: input
+    id: python
+    attributes:
+      label: Python version
+      placeholder: 3.11.7
+    validations:
+      required: true
+  - type: dropdown
+    id: os
+    attributes:
+      label: Operating System
+      options:
+        - Windows
+        - macOS
+        - Linux
+    validations:
+      required: true
+  - type: textarea
+    id: logs
+    attributes:
+      label: Console output / traceback
+      render: shell

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature request
+description: Propose a new feature or improvement
+labels: ["enhancement"]
+body:
+  - type: textarea
+    id: motivation
+    attributes:
+      label: Motivation
+      description: What engineering problem does this solve?
+    validations:
+      required: true
+  - type: textarea
+    id: proposal
+    attributes:
+      label: Proposed solution
+    validations:
+      required: true
+  - type: dropdown
+    id: phase
+    attributes:
+      label: Roadmap phase this fits into
+      options:
+        - "Phase 1 — Core Model"
+        - "Phase 2 — OpenSees Service"
+        - "Phase 3 — 3D Viewport"
+        - "Phase 4 — Modeling Tools"
+        - "Phase 5 — Properties"
+        - "Phase 6 — Analysis Pipeline"
+        - "Phase 7 — Post-processing"
+        - "Phase 8 — Earthquake Engineering"
+        - "Out of scope / new"