fix(pi): treat review as a command, never a session level

[CodeAlex52]

What

resolveSessionMode still accepted review as a session level, so a ponytail-mode entry saved by an older pi version latched: every later turn injected the one-line pointer instead of the ruleset — the state #736 removed from the hooks, #1103 from OpenCode ("a review saved by an older version falls back to the default instead of latching") and #1105 from Hermes.

Fix

pi now only honors runtime levels (off/lite/full/ultra):

• resolveSessionMode skips a review entry, keeps looking, then falls back to the default;
• setMode refuses non-runtime values;
• both fallback normalizations use normalizeMode too, so a review fallback cannot latch either.

/ponytail-review is unaffected — it already runs as a one-shot skill alias, never as a mode.

Tests

• resolveSessionMode drops a review entry saved by an older version (/ponytail-review latches the session mode flag, replacing the ruleset with a pointer line for the rest of the session #736);
• a review entry between two levels is skipped and the latest real level wins.

npm test passes (root suite and pi-extension).