wit: normalize every package to 0.1.0

[mfw78]

What

Resets every WIT package version and use ... @<ver> reference to a single @0.1.0 across nexum:host and shepherd:cow (the videre:* packages were already @0.1.0 post-rename). Deletes docs/migration/0.1-to-0.2.md and the "Migration from 0.1" section in docs/08-platform-generalisation.md, plus the now-dead cross-links to it in docs 00, 01, 02, 04, 05, 07, the ADRs, sdk.md, and diagrams.md.

Why

The @0.2.0 strings were pre-release cruft, not a real compatibility boundary, and no external consumer pins them. After this cut each package versions independently, so the shared baseline needs to be a clean @0.1.0.

Testing

cargo check / cargo clippy --workspace --all-features (nix develop).

AI Assistance

Drafted with AI assistance under human review.

Closes #371

[lgahdl]

The @0.2.0 -> @0.1.0 version-string sweep itself is complete and clean — checked every .wit file and Rust string literal referencing a WIT import path repo-wide, no stragglers.

The migration-doc link cleanup is incomplete, though, in the same way #344 was: docs/05-sdk-design.md still has 4 dangling inline links to migration/0.1-to-0.2.md that this PR doesn't touch (the diff only removes the one reference-list bullet around line 304-309):

• docs/05-sdk-design.md:296 — [migration guide §7](migration/0.1-to-0.2.md#7-sdk-changes-author)
• docs/05-sdk-design.md:436 — [migration guide §2](migration/0.1-to-0.2.md#2-error-model-unification-both)
• docs/05-sdk-design.md:608 — [migration guide §2](migration/0.1-to-0.2.md#2-error-model-unification-both)
• docs/05-sdk-design.md:961 — [migration guide §10](migration/0.1-to-0.2.md#10-deprecation-policy-going-forward-both)

Since this PR deletes the target file, all four will 404 post-merge. Everything else claimed as cleaned up (docs 00, 01, 02, 04, 07, 08, ADR-0001, sdk.md, diagrams.md) checked out fully clean — structurally sound removals, no orphaned headers or broken markdown. Worth a quick follow-up on just these 4 lines before merging.