Show LOC on concluded rankings

[msaroufim]

Summary

• Reintroduce LOC on the main ranking rows for concluded competitions after the Revert "Show LOC on concluded rankings" #250 revert.
• Compute leaderboard line_count after the main ranking query using Python decoding that supports both text and bytea code storage.
• Keep LOC fail-closed: if LOC lookup/decoding fails, the leaderboard response still returns without LOC.
• Keep the simplified surface from Show LOC on concluded rankings #249: no code-drawer LOC plumbing, and concluded leaderboards are no longer blocked by the old 598 special case.

Root Cause

• Production kernelbot migrations store leaderboard.code_files.code as BYTEA.
• The reverted implementation tried to run regexp_replace(cf.code, ...) in SQL, which works on the seed TEXT schema but fails on production-style BYTEA with function regexp_replace(bytea, unknown, unknown) does not exist.

Validation

• Created local kernelboard_loc_test from tests/data.sql and verified /api/leaderboard/339 and /api/leaderboard/340 return 200 with LOC.
• Created local kernelboard_loc_bytea_test from tests/data.sql, applied the kernelbot bytea migration shape to leaderboard.code_files.code, reproduced the old 500, then verified the patched API returns 200 with LOC.
• Ran local Flask server on 127.0.0.1:5055 against the bytea DB and curled /api/leaderboard/339: 200, loc_count=12, sample [56, 56, 56, 56, 56].
• .venv/bin/ruff check kernelboard/api/leaderboard.py kernelboard/api/submission.py tests/api/test_leaderboard_api.py tests/api/test_submission_api.py
• npm run lint
• npm run build
• git diff --check

Notes

• Full pytest was not run because the repo pytest fixture starts Docker Postgres/Redis and Docker is not running in this local environment. The endpoint was tested against local Postgres directly, including a production-like bytea schema.