fix(torghut): dedupe paper route target blockers

[gregkonush]

Summary

• Dedupes paper-route target metadata blocker lists while preserving first-seen ordering.
• Normalizes probe symbols and session import blockers through the same helper.
• Adds regression coverage for duplicated paper_route_runtime_ledger_import_pending and source blocker rows in next-session target plans.

Related Issues

None

Testing

• uv run --frozen ruff format app/trading/paper_route_evidence.py tests/test_paper_route_evidence.py --check
• uv run --frozen ruff check app/trading/paper_route_evidence.py tests/test_paper_route_evidence.py
• uv run --frozen pytest tests/test_paper_route_evidence.py -q
• uv run --frozen pyright --project pyrightconfig.json
• uv run --frozen pyright --project pyrightconfig.alpha.json
• uv run --frozen pyright --project pyrightconfig.scripts.json
• git diff --check

Screenshots (if applicable)

N/A

Breaking Changes

None

Checklist

• Testing section documents the exact validation performed (or N/A with justification).
• Screenshots and Breaking Changes sections are handled appropriately (removed or filled in).
• Documentation, release notes, and follow-ups are updated or tracked.