[code-simplifier] Consolidate repo-root helpers and simplify skill script logic (#9772)

This change simplifies recently touched skill scripts by removing
duplicated repo-root discovery code, promoting shared root lookup to a
public API, and tightening small readability issues without changing
behavior. It keeps script semantics intact while making cross-skill
reuse explicit.

- **Shared API cleanup (`.github/skills/shared/z3db.py`)**
  - Promote `_find_repo_root` to public `find_repo_root`.
- Add `require_repo_root()` for scripts that should fail-fast when root
discovery fails.
  - Update library usage docstring to expose both helpers.
- Replace adjacent SQL string literals in `log()` with a single literal.

- **Deduplicate memory-safety root lookup
(`.github/skills/memory-safety/scripts/memory_safety.py`)**
  - Remove local `find_repo_root()` implementation.
  - Import and use shared `require_repo_root()` from `z3db`.

- **Simplify static-analysis label selection
(`.github/skills/static-analysis/scripts/static_analysis.py`)**
  - Replace two-step label assignment with a single expression:
    - `label = f["type"] or f["category"]`

```python
# before
label = f["category"]
if f["type"]:
    label = f["type"]

# after
label = f["type"] or f["category"]
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

.github/skills/static-analysis/scripts/static_analysis.py

@@ -176,9 +176,7 @@ def print_findings(findings: list):
         return
 
     for f in findings:
-        label = f["category"]
-        if f["type"]:
-            label = f["type"]
+        label = f["type"] or f["category"]
         print(f"[{label}] {f['file']}:{f['line']}: {f['description']}")
 
     print()