fix(orchestrate): encourage parallel work and clarify lead integration

[Tryanks]

Encourage Orchestrate to proactively dispatch work that can advance concurrently, with worker count guided by tasks and dependencies. Remove the existing file-scope restriction from the workflow. The lead integrates parallel deliverables and resolves conflicts.

The lead retains decisions about intent and tradeoffs, along with independent acceptance of the integrated result and discretion over how to perform it. Preserve existing user work and task outcomes. The matching design contract is updated; the implementation remains a focused change to the workflow asset and its documentation.

Validation:

• Based on main in an independent worktree; changes are limited to assets/orchestrate/workflow.md and docs/DESIGN.md.
• Passed git diff --check, cargo fmt --all --check, cargo clippy --workspace --all-targets --locked -- -D warnings, cargo build --workspace --locked, and cargo test --workspace --locked after the final wording correction.
• Direct cargo-machete 0.9.2 found no unused dependencies before the wording correction; Cargo manifests are unchanged. This was the direct binary invocation, not cargo machete.
• Existing environment-dependent tests remain ignored. Mobile/Web and other desktop platforms are left to CI. Existing macOS linker and third-party future-incompatibility notices remain non-failing.
• No new tests or live-model probes were added for this wording change. These checks establish repository compatibility, not guaranteed parallel-dispatch or conflict-resolution behavior.