docs: fix stale file references and missing registry entries

[lauren-h-yoon]

Fixes documentation drift found by auditing each doc page against the current code. No code changes.

Fixes

• adding_a_benchmark.md — built-in task sources register (and set their loader / domain hint) in src/ksi/benchmarks/sources.py, not tasks/registry.py.
• architecture.md — ARC now runs natively: no snapshot mount, no ARC MCP server (arc_load_task), no direct-ARC adapter. Only forum tasks use the direct Anthropic adapter.
• glossary.md — add the command evaluator and custom task source (both used by the quickstart).
• adding_an_evaluator.md — Evaluator.evaluate returns dict[str, Any], matching the protocol.
• custom_tasks/README.md — add the profile-creation step (cp .env.haiku.template .env.haiku) and the Node.js prerequisite.
• scripts/README.md — dataprep/ and arc_prep/ live under benchmarks/scripts/.

Verification

Doc-relevant tests pass (test_docs_contracts, test_cli_flags, test_doctor, test_custom_tasks_example).

[xuefei-wang]

Code review

Found 1 issue:

1. scripts/README.md now points at paths that don't exist. The new scripts/dataprep/ and scripts/arc_prep/ resolve to repo-root scripts/, which has no such subdirectories — the real locations are benchmarks/scripts/dataprep/ and benchmarks/scripts/arc_prep/. The line also contradicts its own clause ("live under benchmarks/") and the preceding sentence at line 5. The commit message states the correct target ("scripts/README.md: dataprep/arc_prep live under benchmarks/scripts/"), so the benchmarks/ prefix looks dropped by accident. benchmarks/README.md uses the bare scripts/dataprep/ form correctly because it is relative to benchmarks/; that form does not carry over to this file.

KSI/scripts/README.md

Lines 17 to 19 in cd16b17

	Benchmark dataset preparation (`scripts/dataprep/`, `scripts/arc_prep/`) and the run presets
	(`run_arc.sh`, `run_polyglot.sh`, `run_swebench_pro.sh`,

Suggested: benchmarks/scripts/dataprep/, benchmarks/scripts/arc_prep/.

Everything else in the PR verified as correct against the code: the src/ksi/benchmarks/sources.py / loaders.py retargeting, the dict[str, Any] evaluator return type, the custom / command registry additions, the ARC-native rewrite, and the Node.js and provider-profile prerequisites.

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[xuefei-wang]

Pushed 3d2eab0 to this branch correcting the path to benchmarks/scripts/dataprep/ and benchmarks/scripts/arc_prep/, which is what the original commit message intended. tests/test_docs_contracts.py passes (3 passed).

The rest of the PR verified clean against the code, so this should be good to merge from my side.

One pre-existing item left alone deliberately, since it is outside this PR's diff: the System Map at docs/architecture.md line 38 still labels memory/mcp_server.py as carrying "ARC toolsets", but that file has no ARC tool handlers. Same drift this PR fixes in the prose below it, if you want it in a follow-up.