docs: add doc comments to all ink! messages in sanctions, version-reg…

[abdoolyaro]

…istry, prediction-market, fractional

• contracts/sanctions/lib.rs: doc comments for the 11 #[ink(message)] entry points that still lacked them (add_sanctioned_entity and remove_sanctioned_entity already had docs from a prior change on main; three newer messages -- set_max_sanctioned_entities, max_sanctioned_entities, active_entity_count -- also already had docs). Covers screening semantics, admin-gating, and notes honestly that screen_property's lookups are not constant-time. (The constant_time_sanctions module referenced in the original issue text has since been removed from this crate entirely by an unrelated upstream change, so that note has been updated to not reference a module that no longer exists.)

  Also fixes one unrelated, pre-existing bug found while verifying this file compiles: a missing closing brace in test_threshold_update_emits_sanction_threshold_updated_event was swallowing the following #[ink::test] fn header into its own body, leaving the file one short overall and preventing the crate from compiling at all on main prior to this change. This is a one-line syntax fix only -- no test logic, assertions, or behavior were changed.

• contracts/version-registry/src/lib.rs: doc comments for all 6 #[ink(message)] entry points, pinning down auto-increment version semantics and how register_deployment_with_version can conflict with or skip ahead of it.

• contracts/prediction-market/src/lib.rs: doc comments for the 8 previously-undocumented #[ink(message)] entry points (set_oracle, create_market, stake_prediction, resolve_market, claim_reward, get_user_reputation, get_market, submit_backtest_data), covering payable status, the reward formula, and the honest admin-driven (not oracle-verified) nature of resolve_market.

• contracts/fractional/src/lib.rs: doc comments for the 4 #[ink(message)] entry points that had none (set_last_price, get_last_price, aggregate_portfolio, summarize_tax). Note: issue Document the fractional public API: 4 of 28 ink! messages lack doc comments #960 named bid_dutch_auction as one of the undocumented four, but it already carries doc comments in the code; the actual gap was in this unrelated group of price/portfolio/tax utility messages.

All changes are additive /// doc comments only, except for the single brace fix noted above; no behavior, error variants, or public signatures were changed.

Verified locally (Windows, pinned nightly toolchain) for all four packages:
cargo doc -p propchain-sanctions --no-deps && cargo test -p propchain-sanctions (9 passed)
cargo doc -p version-registry --no-deps && cargo test -p version-registry (8 passed)
cargo doc -p propchain-prediction-market --no-deps && cargo test -p propchain-prediction-market (10 passed)
cargo doc -p fractional --no-deps && cargo test -p fractional (50 passed)
Rebuilt against current main (24fac29) after that verification to
resolve a merge conflict in contracts/sanctions/lib.rs and to pick up
the fix for the missing-brace bug described above; re-verify before
merge.

Closes #957,
Closes #958,
Closes #959,
Closes #960.

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[nanaf6203-bit]

LGTM