v0.25.1 — validate 0.25.0 env knobs

Hardening for the v0.25.0 opt-in image features (delta-audited, adversarially verified). Both findings low/quality, same root cause: bare Number(env || default) doesn't catch a malformed value.

• fix(image) — a typo'd numeric env became NaN and silently changed behavior: BLOCKRUN_CONFIRM_THRESHOLD="$0.05" flipped the confirm gate to ask-on-every-call, and (fail-open) a malformed BLOCKRUN_INLINE_MAX_BYTES removed the inline base64 context cap (data.length > NaN is always false). confirm-spend now reuses the validated parseBudgetLimitEnv; inline-image uses a validating envInt (falls back on non-finite/non-positive, clamps quality 1–100). No change for valid configs.

84 unit tests. Full details in CHANGELOG.md.