Replace bare except clause with specific exception handling

[Copilot]

Addresses code review feedback on PR #116 regarding a bare except: clause that silently catches all exceptions without explanation.

Changes:

• Replace except: with except (TradeMatch.DoesNotExist, AttributeError): to catch only expected exceptions
• Add explanatory comment documenting the fallback behavior

Before:

try:
    trade_match = TradeMatch.objects.get(pk=match_id)
    timetable_slug = trade_match.request_1.offered_allocation.timetable.slug
except:
    pass

After:

try:
    trade_match = TradeMatch.objects.get(pk=match_id)
    timetable_slug = trade_match.request_1.offered_allocation.timetable.slug
except (TradeMatch.DoesNotExist, AttributeError):
    # Silently ignore if trade match doesn't exist or lacks required attributes
    # We'll fall back to redirecting to '/' instead
    pass

This prevents inadvertently catching system-critical exceptions while making the code's intent explicit.

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