chore: homogenize all crate versions to 0.1.0 via workspace.package

[mfw78]

Final end-of-train pass (M5, the three-repo release baseline). Do NOT land mid-train - a workspace-wide version + Cargo.lock change would conflict with every remaining car. Runs once the three-repo split (nexum/, videre/, shepherd/) has landed.

Four crates carry a drifted 0.2.0 while everything else is 0.1.0: nexum-runtime, nexum-cli, nexum-launch, shepherd (plus shepherd-cow-host pre-split, which becomes videre-host at 0.1.0). The 0.2.0 reflects the pre-release 0.1 -> 0.2 runtime evolution, but corresponds to no git tag, no release, and no inter-crate version pin, so resetting to a coherent 0.1.0 baseline is safe.

Root cause: [workspace.package] hoists edition / license / repository but not version, so each crate pins its own and these drifted - the exact failure mode the block's own comment already names.

Change

• Add version = "0.1.0" to [workspace.package].
• Convert the core crates (crates/ + tools/, across all three groups) to version.workspace = true.
• Leave guest modules under modules/ on an explicit 0.1.0 (standalone-authorable; a module author has no access to the workspace table, per the existing convention).
• Regenerate Cargo.lock.

Acceptance criteria

• No crate pins 0.2.0; every core crate resolves to 0.1.0 via version.workspace = true.
• cargo metadata shows a single 0.1.0 across the workspace, modules included.
• Green fmt / clippy / test.