Tasks: `graph status` reads the state file the runtime wrote

Phase 4 of 4. Each task names the requirement it satisfies and the testing-plan row that proves it; the test lands with the change (red first).

Task list

[x] A1 — core.graphs.work_item_id. Ref → issue-<n> through WorkItemRef.parse and graphlink.spec_id_for; applied first in every core graph verb. Req: R1.1, R1.4 · Test: T1.
[x] A2 — StatusReport names its state file. state_path/state_found filled by Runtime.status; statePath/stateFound in as_dict; the issue-238 key-set test updated; API and MCP docstrings and the authored OpenAPI description. Req: R2.2 · Test: T1, T3. Deps: none.
[x] B1 — the CLI resolves the checkout and prints the path. --repo unset on check and graph; _resolve_root (registry lookup for the read verbs); _state_line; the repo: note. Req: R1.2, R1.3, R1.4, R2.1, R2.3 · Test: T2, T7. Deps: A1, A2.
[x] C1 — docs and evidence. README.md (graph status <id|ref>), docs/cli/commands/graph.md and check.md (the ref form, --repo unset, the state: line), docs/capabilities/process-graph.md and cli.md (requirement + history rows), the e2e report's B7/O6 and the follow-ups index link the issue; evidence files. Deps: A1–B1.

After A1 + A2: tests/test_core_graphs.py and tests/test_api_contract_parity.py green.
After B1: tests/test_graph_status_resolution.py green.
After C1: full suite, ruff, pyright, markdownlint.

None yet.