fix(healthcheck): replace broad exception handler with specific types

[bugman-007]

Summary

• Replaces except Exception: with specific exception types
• Complies with CLAUDE.md: "Narrow exceptions at I/O boundaries are fine" but "No broad or silent catches"
• Makes error handling explicit and debuggable

Changes

• body.decode() (line 216): except (UnicodeDecodeError, AttributeError) instead of except Exception

Rationale

The original code used a broad except Exception: handler when decoding HTTP response bodies. The decode operation has two specific failure modes:

1. UnicodeDecodeError - malformed bytes that can't be decoded as UTF-8
2. AttributeError - body is not bytes (e.g., already a string)

Both map to the same fallback behavior: str(body). Making these explicit improves debuggability.

Test plan

• Python syntax check passes
• Manual test: healthcheck handles malformed UTF-8 in response body
• Manual test: healthcheck handles non-bytes response body

[Lightheartdevs]

Closing as part of v2.1.0 stabilization. We're pausing new feature PRs while we solidify the installer and CI gates. If this is still relevant for v2.2.0 (targeting April 1), please rebase and resubmit. Thank you for contributing.