feat(*): add an experimental Curator that cultivates harness-of-harnesses workers

[tzteyang]

Summary

Adds experimental/, a first version of worker RSI: a Curator that shapes a
Raven worker's harness from the task, the materials handed to it and feedback,
the way a new employee is trained.

The worker is a harness-of-harnesses. A root Raven harness faces the user and
calls child harnesses, each a full Raven agent hosted over ACP, through the
nodes of its playbooks. Every harness has the same four strategy facets
(memory, planning, capability, action). The Curator reads the actual harnesses
and generates code and config on those facets at both levels: the root
candidate sets the playbooks and writes per-node requirements, each child is
curated against the requirements of its nodes, and the set is checked on
copies and activated together.

Layout:

• curator/: staged generation (understand, select, design, implement,
  repair), two-level composition, harness contracts, and raven_adapter/,
  the only layer that touches a worker's Raven runtime
• analyst/: turns an evaluator's words and execution records into
  observable behavior requirements
• iteration/: the generic loop (onboarding curation, then trial, review and
  curation each round) and a CLI for a human evaluator
• simulation/: a simulated travel agency that runs the loop, plus one
  showcase case (simulation/cases/s0925c/: case notes, the exported
  transcript split by phase, and the round 1 and round 3 decks)
• docs/design.md (structure, curation flow, composition sequence, the Raven
  connection) and docs/rsi-iteration.md (the loop and the Analyst)

Key decisions:

• No change under raven/, and raven/ does not import experimental/.
  Generated artifacts land on Raven's existing extension points. The few Raven
  internals the adapter reads are listed in docs/design.md section 5.4.
• The Curator explores a read-only source snapshot; the caller names the
  evaluation side to withhold from it, so the generic layers name no scenario.
• The single-layer owner analysis is kept only to reproduce the showcase case
  and is marked for removal; the two-layer Analyst is the default.
• The two decks are .pptx files of about 230 KB each. They pass
  check-large-files; flagging them in case they count as report assets
  under AGENTS.md section 7, in which case they can move out of git behind a
  link.
• One follow-up for Raven 0.2.2: playbooks in prompt and rounds modes ship no
  fixed nodes, so node requirements are read from dag playbooks only.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

On the branch rebased onto the latest main:

• uv run pytest tests/test_harness_curator_*.py tests/test_analyst_*.py tests/test_iteration_*.py tests/test_simulation_*.py -q: 368 passed

• uv run pytest -m integration tests/integration/test_harness_curator_*.py --deselect tests/integration/test_harness_curator_real_llm.py -q
  (offline, stub providers): 57 passed

• uv run pytest -q (whole suite, with the host proxy variables unset and
  PYTHONTZPATH set): 26692 passed, 2 failed. One was an order-dependent test
  of this PR and is fixed here; the other,
  tests/test_subagent_node_runtime.py::test_what_cannot_be_read_names_nothing,
  fails only because the machine runs as root and is unrelated.

• uv run ruff check and uv run ruff format --check on the touched files:
  clean

• scripts/check_large_files.py origin/main..HEAD,
  scripts/check_source_language.py origin/main..HEAD,
  scripts/check_commit_messages.py origin/main..HEAD and
  npx commitlint --from origin/main --to HEAD: all exit 0

• Relevant tests pass locally

• Relevant lint / type checks pass locally

• User-facing docs or screenshots are updated when needed

Risk

No user-visible change for Raven: experimental/ is not imported by
raven/ and is not packaged in the wheel (packages = ["raven"]).
CONTEXT.md gains one glossary entry. The Curator's exploration offers a
shell only under an OS sandbox executor. Rollback is a revert of the squash
commit; nothing else depends on experimental/.

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

Related Issues

N/A