fix: resolve duplicate Alembic revision IDs causing missing oidc_subject column

[boludo00]

Root cause

Two pairs of migration files had duplicate revision IDs:

File	Old revision	New revision
031_add_direct_download_settings.py	031	031b
032_add_library_mapping_to_booklore_servers.py	032	032b

When Alembic loads the versions/ directory it errors on duplicate revision IDs. The entrypoint.sh caught this with || echo "WARNING: Alembic migrations had issues" and continued, so migration 035 (which adds users.oidc_subject) never ran, producing:

sqlalchemy.exc.ProgrammingError: (psycopg2.errors.UndefinedColumn) column users.oidc_subject does not exist

Changes

• 031_add_direct_download_settings.py — revision 031 → 031b
• 032_add_flaresolverr_url.py — down_revision 031 → 031b (keeps the direct-download chain intact)
• 032_add_library_mapping_to_booklore_servers.py — revision 032 → 032b
• 034_merge_heads.py — updated down_revision to ('031', '031b', '032b', '033') so all four branch heads are merged
• 035_add_oidc_fields.py — made idempotent (skips add_column/create_index if they already exist), defensive against databases bootstrapped with create_all
• entrypoint.sh — two improvements:
  1. Detects legacy databases that have schema but no alembic_version table and stamps them at the correct revision (034 if oidc_subject is missing, heads if fully current) before running upgrade heads
  2. Fails loudly (exit 1) on migration errors instead of masking them

Test plan

• Fresh container start against a new PostgreSQL database — all 36 migrations apply cleanly, app boots
• Container start against a database stamped at 034 (missing oidc_subject) — migration 035 runs and adds the column
• Container start against a database with tables but no alembic_version and no oidc_subject — entrypoint stamps at 034, then 035+036 run
• Container start against a fully current database — no migrations run, app boots normally