flight_seam_differential.py broken on main: looks up 'func_0', absent since the #394 name work — dev-script drift not caught by CI

[avrabe]

Found by the VCR-RA-001 spike agent (PR #569) while running flag-on differentials: scripts/repro/flight_seam_differential.py fails on current main flag-off too — it looks up symbol func_0, which no longer exists after the #394 name-propagation work (functions now carry export/name-section names in the paths the script reads).

Two things to fix:

1. The script: resolve symbols the robust way (pyelftools SHT_SYMTAB, matching the current naming priority) — same class as the earlier host-dependent synth disasm lesson (PR ci(vcr-oracle): CI-gate the RV32 immediate-shift-fold execution oracle (#472, #242) #489).
2. The gap it reveals: this differential is a dev script, NOT CI-gated — so it drifted silently when naming changed. Either CI-gate it like the other execution oracles (preferred; the flight_seam fixture is load-bearing) or mark it deprecated in favor of the CI-gated frame_slot_dce_differential.py which covers the same flight_algo anchor (0x07FDF307).

Note: emitted code is NOT affected — CI-gated differentials (const_cse, frame_slot_dce) pass on the same fixtures; this is harness drift only.