v2 Stage 5: docs, versioning, hand-off

[rahlk]

Part of #69.

Stage 5 — docs, versioning, hand-off

Branch: feat/v2-stage5-docs-release

Deliverables:

• README.md rewrite: v2 model + four levels + Architecture & Tooling (incl. the Scalpel decision); drop the "queryable slicer" product framing.
• CLAUDE.md + AGENTS.md rewrite describing schema v2 in detail (verify git ls-files AGENTS.md; un-ignore if the global gitignore hides it).
• .claude/SCHEMA_DECISIONS.md v2 entries: can:// grammar, synthetic-vertex of/var vocabulary, Scalpel oracle.
• Regenerate schema.neo4j.json at 2.0.0; update test_neo4j_schema.
• CHANGELOG.md + MAJOR version bump in pyproject.toml; regenerate the README --help block.
• Hand-off bundle (docs/handoff/): sample analysis.json per level + a graph.cypher; the schema contract; the CLI --help; the published package name + version to pin (for the separate cldk-sdk-frontend follow-up).

Gate: full suite green (pytest test/ -q); --emit schema yields 2.0.0; hand-off bundle present.

Expand into full bite-sized tasks with superpowers:writing-plans at stage start.

[rahlk]

Stage-5 schema task (surfaced in Stage 3 Task 3.6): the Neo4j CPG emitter now writes PY_DDG.prov (list), but the neo4j/schema.py catalog declares PY_DDG with only var. Runtime-harmless (Neo4j props are schemaless; the catalog only feeds --emit schema + the currently-skipped test_neo4j_schema). When re-enabling test_neo4j_schema in Stage 5: add prov: "string[]" to the PY_DDG RelType, regenerate schema.neo4j.json, and MAJOR-bump the Neo4j SCHEMA_VERSION to 2.0.0.

[rahlk]

Additional Stage-5 schema-regen cleanup (Task 4.6): the PyCFGNode NodeLabel in neo4j/schema.py declares a dead of: "string" prop that the emitter never produces (it maps BodyNode.of → the var prop). Drop the of declaration before regenerating schema.neo4j.json, else it surfaces to SDK consumers as an always-null queryable property. (The call_node int→string retype landed in 4.6 is correct — keep it.)