parser: harden possessive participle classifier (#808 followup)

[MichaelMillsOfficial]

Follow-up to #808 (Yuriko, the Tiger's Shadow). Addresses Gemini review feedback on `parse_possessive_participle` / `parse_possessive_object_type` in `oracle_quantity.rs`.

Changes

1. Decompose the object-type combinator

Replace the verbatim 9-string `alt(tag(...))` with `opt(parse_supertype_prefix) + alt(singular_type_words ∪ token)`. Reuses `oracle_nom::target::parse_supertype_prefix` (CR 205.4a) so composed forms like `"the sacrificed legendary creature's power"` parse via the supertype × type axis instead of the cartesian enumeration. Adds the `token` referent (CR 109.1 / CR 110.5) which is not a CR 205 card type but anchors real possessive references.

2. Extend the participle list

Add `milled` (Court of Cunning, Patchwork Automaton, Demilich class) and `discovered` (LCI Discover mechanic). These are the two missing participle-possessive cost / trigger-condition referents Gemini called out.

3. Lock the word-boundary invariant with regression tests

The determiner gate (`"that "` / `"the "`) in `classify_possessive_referent`, combined with `all_consuming((participle, tag(" "), object_type))`, already guarantees that player-possessives (`"an opponent's ..."`) cannot match the participle branch. New tests pin both halves of the contract — positive composition tests for the new participles + supertype + token cases, and negative tests for `"an opponent's"` and plural `creatures'` prefixes.

Sample card texts now covered

• `"the milled card's mana value"` → `ObjectManaValue { CostPaidObject }`
• `"the discovered card's mana value"` → same
• `"the sacrificed legendary creature's power"` → `Power { CostPaidObject }` (via supertype composition)
• `"the sacrificed token's power"` → same
• Negative: `"an opponent's life total"`, `"the sacrificed creatures' power"` → `None`

Verification

• `cargo fmt --all`: clean
• `cargo clippy --all-targets -- -D warnings`: clean
• `cargo test -p engine --lib parser::oracle_quantity`: 112/112 pass
• `./scripts/gen-card-data.sh`: success
• `cargo coverage`: 85.33% (29670 / 34770), unchanged

🤖 Generated with Claude Code

[gemini-code-assist]

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