Add optional Jev web decision handoff to Python client

[AetherAI3]

Purpose

Add an optional Jev → selected-model decision handoff for the Python client. Jev makes bounded navigation choices over caller-approved URLs; the host application's chosen model handles reasoning and generation. Explain the split and privacy boundary in the root README and Python README.

Exact scope

• Base commit: 9981040b2e873b4120d0bc57850cbbb917603708
• Exact head commit: 9b2e1aa2a3bae38ca01c9f306278e02f7dfd3434
• Allowed paths: README.md, clients/python/README.md, clients/python/src/aether_browser/jev.py, clients/python/tests/test_jev.py, docs/JEV.md
• Non-goals: browser-server authority changes, npm parity, MCP tools, autonomous clicking/forms, bundled generative model, releases, deployment
• Contract references: OpenRouter Jev System One/Decisions Choice envelope and TypeSafe text-only model documentation (linked in docs/JEV.md)
• Dependency PRs: none

Verification

• PYTHONPATH=clients/python/src python -m unittest discover -s clients/python/tests -v — 53 passed, including 8 Jev tests.
• python -m compileall -q clients/python/src/aether_browser/jev.py — passed.
• git diff --cached --check — passed before commit.
• Live provider integration was not run (no provider key in this environment); provider contract is exercised with a fake transport. Repository CI for this exact head passed all six jobs: change-map, quality, unit, security, node-client, and python-client.

Security and privacy

No browser-server security-boundary change. The optional Python client sends caller-selected text, goal, URL/title, and up to three candidate URLs to OpenRouter using a caller-owned key. It sends no screenshots, follows no provider redirects, accepts only the pinned Choice schema/model, and cannot invent a destination. The existing browser server still enforces navigation policy. Common login/payment signals cause human takeover before sending page text; callers must also filter sensitive text and signed URLs because this detector is necessarily incomplete. There are no new dependencies, listeners, containers, or CI permissions.

Rollback

Revert this commit; no server or persisted state migrates. Any already-sent provider requests remain in the provider's records according to the caller's account settings.

Confidence and unknowns

• Confidence: client behavior and bounded failure paths are covered by unit tests.
• Known limitations: no visual interpretation or safe click selectors from the current browser response, Python-only opt-in module, caller supplies the reasoning model.
• Follow-up: live provider smoke test with an authorized key and measured decision latency/cost before a hosted product rollout.

Checklist

• The branch is based on the declared commit and the exact head is recorded above.
• Public behavior and documentation agree.
• Tests cover the changed contract and its denial or cleanup path.
• No secrets, private host details, personal data, or private page content are included.
• No dependency or hash-lock change.
• The change does not publish the repository, Pages, a release, or a hosted service.
• CI evidence belongs to this exact head and no valid review finding is unresolved.