fix(parser): recover multi-target spec for tap/untap up-to phrases

[andriypolanski]

Summary

Elder Deep-Fiend's "When you cast this spell, tap up to four target permanents" was parsed as a single-target tap effect because the imperative parser stripped the "up to four target" quantifier but never stamped MultiTargetSpec onto the ability. At cast time the engine surfaced a malformed TriggerTargetSelection (one mandatory slot instead of up to four optional slots), which could crash the React client with a blank blue screen.

This PR adds two post-parse recovery helpers in oracle_effect/lower.rs, mirroring the existing extract_exact_target_multi_target / extract_bounded_target_multi_target pattern:

• extract_optional_target_multi_target — recovers "tap up to four target permanents" and the full MULTI_TARGET_VERBS class (exile, tap, untap, goad, return, destroy, choose).
• extract_verb_up_to_multi_target — recovers non-target-word shapes like "untap up to five lands" (Peregrine Drake class) via the existing strip_any_number_quantifier building block.

Closes #3274

Root cause

The Fight imperative path already preserved multi_target through TargetedImperativeAst::Fight and a lower_imperative_family_ast intercept. Tap/Untap imperatives called strip_optional_target_prefix but discarded the returned spec. The ability lowerer only recovered exact-count and bounded-count phrases, not "up to N target …".

Changes

File	Change
crates/engine/src/parser/oracle_effect/lower.rs	Add extract_optional_target_multi_target, extract_verb_up_to_multi_target; wire into ability-definition lowering; unit tests
crates/engine/tests/integration/issue_3274_elder_deep_fiend.rs	Parser + runtime regression tests
crates/engine/tests/integration/main.rs	Register new integration module

Test plan

• extract_optional_target_multi_target_recovers_tap_up_to_four (unit)
• extract_verb_up_to_multi_target_recovers_untap_lands (unit)
• elder_deep_fiend_cast_trigger_parses_up_to_four_multi_target — AST carries MultiTargetSpec::up_to(4)
• elder_deep_fiend_cast_trigger_surfaces_four_optional_target_slots — casting with ≥4 legal permanents yields four optional TriggerTargetSelection slots
• Manual: cast Elder Deep-Fiend (normal or Emerge) in browser; confirm targeting overlay accepts 0–4 permanents without blank-screen crash

Closes

Fixes #3274

[gemini-code-assist]

Warning

You have reached your daily quota limit. Please wait up to 24 hours and I will start processing your requests again!

[matthewevans]

VERDICT: approve

Parser/runtime regression reviewed clean, maintainer/contributor clippy fix is limited to the test pattern, CI is green, and the current head is labeled bug.