standards: add workspace and CI split

[HDauven]

Part 1 of the Dusk standards stack.

Adds the plumbing needed to host Dusk contract standards without coupling them to the legacy genesis/test contract workspace:

• creates a separate standards/ Cargo workspace
• adds a minimal dusk-contract-standards crate shell
• restores the root workspace to legacy genesis/test contracts only
• keeps legacy dependencies on their existing compiler-compatible versions
• adds standards Makefile targets
• path-gates CI so standards changes run standards CI while legacy genesis checks stay isolated
• keeps CI jobs on core

This PR intentionally does not add standards behavior yet. It is the foundation for the following stacked PRs.

Validation:

• make standards-ci

[moCello]

REQUEST CHANGES — CI path filter classifies shared root files as standards-only, so legacy clippy/test skip on this PR (confirmed via gh pr checks) despite the toolchain bump; README ships dead links to docs/ and standards/examples/; standards-data-drivers references an undefined make variable and breaks standards-hardening.

[moCello]

APPROVE — all four prior-round blockers fixed cleanly (dorny/paths-filter adopted with shared roots in both filters, README dead links removed, STANDARDS_EXAMPLES defined and guarded, root toolchain pin preserved); one NOTE on filter-list duplication is hygiene, not blocking.

[HDauven]

Thanks. I opened #34 to track the remaining non-blocking filter-list hygiene note before merging this PR.