chore(release): prepare v0.21.1

[bkearns]

Prepares the corrected stable Ferrosa release after the rejected v0.21.0 build exposed a future-incompatibility warning.

This is a mechanical version-only change:

• workspace package version 0.21.0 -> 0.21.1
• all 26 publishable workspace lock entries 0.21.0 -> 0.21.1
• no third-party dependency movement
• private xtask remains 0.17.0 with publish disabled

The tabled derive dependency fix from PR #378 remains present, and the resolved graph contains neither tabled_derive nor proc-macro-error2.

Verification:

• independent PASS, no blockers
• all publishable workspace packages resolve 0.21.1
• cargo check -p ferrosa -p ferrosa-ctl --features ferrosa/full: green, zero warnings
• dependency feature regression: green
• cargo fmt and git diff --check: green