fix: correctness pass on Blender skills, snippets, and docs

[TMHSDigital]

Summary

Correctness pass across skills, snippets, and docs. No content added or removed, so aggregate counts are unchanged (validate-counts stays green).

Code bugs (what the AI serves users)

1. operators/SKILL.md — OBJECT_OT_offset_active called bpy.types.Vector(offset); Vector lives in mathutils. Added from mathutils import Vector and use Vector(offset). Also column-normalized the basis (matrix_world.to_3x3().normalized()) so object scale no longer distorts a local-axis direction.
2. cross-version-property-delete.py — property_unset() resets a registered RNA prop to default; it does not remove a custom ID property. Dropped the bpy.app.version branch; del id_block[key] is version-stable on all versions. Header now documents the distinction so readers don't reintroduce it.
3. version-branch-skeleton.py — clear_property() used property_unset as a "divergence" example, but del works on both 4.5 LTS and 5.x (not divergent). Now del obj[key] unconditionally; get_eevee_engine_id() remains the genuine divergence example.
4. custom-properties/SKILL.md — Removed the "(or property_unset() on 5.0+)" parenthetical from the unbind example and rewrote the "Compatibility paths" section. Both unbinding a type-level PointerProperty and removing an ID property are version-stable via del; property_unset is explicitly called out as a different operation.
5. shader-node-group.py — Modernized ShaderNodeMixRGB → ShaderNodeMix with data_type='RGBA', consistent with the geometry-nodes-python skill. Verified against the ShaderNodeMix docs: the node shares socket names (Factor/A/B/Result) across every data type, so name lookup is ambiguous — wired the RGBA sockets by index (inputs[0] Factor, inputs[6] A, outputs[2] Result).

Doc drift

6. README.md — Removed the hardcoded version-0.2.0 shields badge that drifts every release. The dynamic github/v/release badge already covers it (root-cause fix, not a re-hardcode).
7. ROADMAP.md — v0.2.0 row status **Current** → Shipped and dropped the per-row marker, so the action-owned **Current:** prose line is the single source of truth. The **Current:** line itself was not touched.
8. SECURITY.md — Supported Versions 0.1.x → 0.2.x; scope text "one ... template" → two templates.
9. CONTRIBUTING.md — Snippet length 5 to 30 → 5 to 50 (matches README/CLAUDE). Replaced hardcoded 1.9.1 standards-version markers with a pointer to the meta-repo STANDARDS_VERSION, and fixed wording from VERSION to STANDARDS_VERSION (the two are decoupled).
10. CLAUDE.md — Relabeled the 7 materials/drivers/migration snippets from v0.2.1 to v0.2.0 to match ROADMAP/CHANGELOG/README. The **Version:** line was not touched.

Flag for a separate meta-repo look

The v0.2.0 → v0.2.1 mangling of historical snippet text in CLAUDE.md looks like the release-doc-sync step running a find/replace that caught a non-current version reference. Worth auditing the action so it only rewrites the current-version prose and leaves historical attributions alone.

Out of scope (per request)

• No standards-version markers in live files touched (left at 1.9.4); no .github/workflows changes — owned by the separate fleet-onboarding op.
• Action-owned lines untouched: CLAUDE.md **Version:**, ROADMAP.md **Current:**, CHANGELOG.md.

Test plan

• python -m py_compile on all three edited snippets passes.
• Aggregate counts unchanged → validate-counts green.
• No stray property_unset/ShaderNodeMixRGB/bpy.types.Vector/version-0.2.0 references remain.