Extends WT-17974 with KILL_FOLLOWER crash recovery. Validates that both the leader and follower homes recover correctly after the follower is killed.

Add KILL_FOLLOWER mode to the test from WT-17974:

• Parent sends SIGKILL to the follower after at least one checkpoint pickup completes.
• Leader continues running until the parent kills it after the follower exits.

Verification:

• Leader home: open with disaggregated=(lose_all_my_data=true), query last_disaggregated_schema_epoch as the epoch cutoff, replay leader per-thread record files up to the cutoff as in WT-17972.
• Follower home: open as leader for recovery so the page log checkpoint populates last_disaggregated_schema_epoch, then replay follower per-thread record files up to the cutoff using the same verification logic.

Deliverables:

• Extend test/csuite/schema_disagg_leader_abort/ from WT-17974 with KILL_FOLLOWER kill mode and dual-home verification in main.c and verify.c.
• Evergreen stress variant in test/evergreen_disagg.yml with extended run time.