fix: add label() to qualified column names in JOIN SELECT to prevent ambiguous column errors

[halconel]

Summary

Fixes remaining issues with reverse join and changelist processing after PR #368.

Changes

1. Fix ambiguous column errors in JOIN queries (commit 554f7bd)

Problem: JOIN queries generated qualified column names in SELECT (e.g., primary_meta_tbl.id) without aliases, causing "column reference 'id' is ambiguous" errors in WHERE clause.

Solution: Added .label(k) to all qualified columns in SELECT:

# Before: SELECT primary_meta_tbl.id FROM ...
select_cols.append(primary_meta_tbl.c[k])

# After: SELECT primary_meta_tbl.id AS id FROM ...
select_cols.append(primary_meta_tbl.c[k].label(k))

Modified functions:

• _build_reverse_meta_cte
• _build_reverse_data_cte
• _meta_data_sql_helper

2. Use offset=0 for changelist with reverse join support (commits 0e5b668, cb495f2)

Problem: Initial approach (commit 5b1a19a) disabled offset optimization entirely by switching to v1, which broke reverse join functionality.

Solution: Use v2 (with reverse join support) but with offset=0 for all tables:

• Added changelist_mode flag in get_change_list_process_ids
• build_changed_idx_sql_v2 checks this flag and uses offset=0 instead of saved offsets
• This allows reverse join to work while processing all records from filters_idx
• Fixed ambiguous column error in reverse join by passing ref_meta_tbl to _apply_sql_filters
• Filter only columns that exist in table in sql_apply_filters_idx_to_subquery

Benefits:

• ✅ Reverse join with join_keys works in changelist
• ✅ No offset filtering (processes all records specified in changelist)
• ✅ Maintains v2 architecture and performance

3. Add production test case (commit 43eaf2c)

Added comprehensive test reproducing the exact production scenario that caused the bug:

• Primary table: advertising_campaign_to_moderate
• Reverse join with composite keys: id + ad_campaign_id
• Reverse join with single key: id only
• Transform keys spanning multiple tables

Testing

✅ All changelist tests pass
✅ Offset optimization works correctly in run_full
✅ Reverse join with filters_idx works without errors
✅ Production case with composite join_keys passes