V175 targeted validation

PASS - live DRAKEXP.lua snapshot lists only .chr stems from the active account folder
PASS - switching account replaces the snapshot with only the new account's character names
PASS - logout clears the snapshot
PASS - Export UI reads DRAKEXP.lua directly
PASS - existing row selection fills the editable export filename field
PASS - rename/new export remains enabled
PASS - Import Character File path unchanged
PASS - Import Saved Game / pregenerate remain disabled
PASS - UI patcher remains idempotent for the Export pulse
PASS - installer smoke test creates DRAKEXP.lua and embeds the V175 runtime
PASS - Python source compilation

No CHR/BIO backup or restore logic was added.
