feat(cli): --if-exists for localizations update and web apps create

Summary

Two 409 hotspots are not covered by the --if-exists series (#2579, #2583, #2584, #2586, #2592): asc localizations update (109 installs with 409 in 14 days, 28 in the last 48 h) and asc web apps create (39 conflicts among 156 installs, 58% failure rate).

What to do

Follow the convention from #2579: match Apple's 409 codes across every errors[] entry (asc.APIError.AllCodes), then a decisive read-back; skip returns an additive receipt, update routes to the matching write, fail is unchanged. For web apps create the conflict is a Developer Portal / Iris response, so capture the real conflict body from fixtures or a recorded session and key on it; if the web path cannot be read back safely, implement skip only and say why.

Acceptance criteria

• RED httptest with the real 409 body per command
• default behavior byte-identical
• stacked on the core branch until #2579 merges, then retargeted