Add watched AI-agent control-lease for Workbench live sessions

[ds-code-t]

Summary

Workbench is a collaborative live-testing space. This adds a controller-owned control lease so a human can watch an AI agent work in the same Swing window, then take the floor at any time. Swing and MCP/HTTP attach remain adapters over WorkbenchServices / WorkbenchController / LiveScenarioPlayer. There is still one Workbench JVM and one consumer worker.

Behavior

• Lease holder is HUMAN (default when the UI is up) or AGENT, plus agent display name, currentAction banner text, and an optional pending Save permission.
• Agent mutating calls fail until workbench_request_control. While the agent holds the lease, Swing play/edit/mapping/save/worker controls lock. WebView editors stay mounted and become read-only. Take control stays enabled, returns HUMAN, and fails in-flight agent permission waits.
• Testing the live scenario (executeStep, play, Mapping reads, evidence) is allowed on the agent lease. Copying into the original .feature is not.
• Human Save asks before copying the live scenario into file X / scenario Y. Agent Save uses the same service and, with the UI attached, blocks on Allow/Deny. Deny writes nothing. The demo buffer stays unsavable. Picker load still never rewrites features.
• UI mode cannot share stdout with stdio MCP, so ui starts a 127.0.0.1 JSON attach endpoint and writes .pickleball/workbench/attach.json (url + token). Headless mcp stdio is unchanged: stdout remains JSON-RPC only. That client may hold the lease without a banner; Save is still an explicit tool.

Functionality-change coverage

• I reviewed AGENTS.md and the relevant feature-map entry.
• Framework implementation is complete.
• Focused framework tests were added or updated.
• Maven consumer scenarios were not added. This is Workbench-controller behavior; coverage is headless Workbench unit tests rather than @all Cucumber.
• Canonical documentation was updated (docs/pickleball-workbench.md, docs/pickleball-workbench-player.md, pickleball-workbench/AGENTS.md).
• docs/agent/feature-map.md remains accurate.
• docs/agent/repository-index.md is current.
• Backward compatibility was preserved, with one documented stdio contract addition: mutating MCP tools now require workbench_request_control first. The stdout JSON-RPC-only contract is unchanged.

Validation

• python3 scripts/verify_agent_contract.py
• python3 scripts/refresh_agent_index.py --check
• python3 scripts/sync_consumer_guidance.py --check
• ./gradlew :pickleball-workbench:test (includes verifyWorkbenchMcpStdio and artifact checks)
• ./gradlew verifyStrictControllerIsolation
• Root ./gradlew test not run; this is a Workbench-only change.
• ./gradlew publishToMavenLocal not required to land the 2.1.9 Workbench controller.
• Maven consumer @all not run, per Workbench validation policy.

This PR targets 2.1.9, not master. After validation it is merged into 2.1.9.