Unify hosted rollout task targeting

[solvemproblr]

High-level idea

Make hosted SDK rollouts use the platform canonical single-rollout contract while preserving exact identity for unchanged synced tasks.

Companion platform PR: https://github.com/hud-evals/hud-monorepo/pull/1407

Issue

The SDK previously submitted every task by environment, scenario, args, and slug. The platform then tried to reverse-match that content to a task version, which was ambiguous and caused locally modified tasks to be conflated with synced versions.

Solution

• Retain the platform task-version ID and a content signature when loading taskset exports.
• Submit unchanged platform tasks as explicit task-version targets.
• Submit new or locally modified tasks inline, without an implicit sync or taskset link.
• Send model and max-steps through the canonical rollout request fields.

Impact

Synced tasks remain attached to their exact stored version; dirty and tasksetless tasks still run remotely as standalone inline work. This PR is stacked with the companion hud-monorepo rollout API change.