Add consumer-agent investigation HTML handoff

[ds-code-t]

Summary

After a live isolation loop and one diagnostic mvn test, a consumer agent can emit a small human handoff under the consumer project:

.pickleball/investigations/<id>/
    investigation.json    # source of truth
    report.html           # one-page local render

In chat the agent prints only the project-relative report.html path. JSON is the source of truth. HTML renders that JSON plus at most two screenshots linked from the existing diagnostic pack. The diagnostic run is not copied, pkb_diagnostic_output is unchanged, and there is no PDF.

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 and supporting resources were added or updated when applicable.
• README or canonical documentation was updated when behavior changed.
• docs/agent/feature-map.md remains accurate.
• docs/agent/repository-index.md is current.
• Backward compatibility was preserved, or the breaking change is documented.

Implementation

• JDK-only InvestigationHandoff in pickleball-control-protocol so DiagnosticCli and Workbench emit identical reports without giving Workbench a core Pickleball dependency.
• DiagnosticCli emit-investigation <investigation-json-or--> <consumer-project-root> writes the pair and prints the relative HTML path.
• MCP workbench_investigation_emit on the same WorkbenchServices / WorkbenchController seam as workbench_diagnostic_catalog. Sparse result: { "reportPath": "..." }.
• export-guidance never manages or deletes .pickleball/investigations/.
• AGENT-GUIDE live loop/tool chooser: emit, then print only .pickleball/investigations/<id>/report.html. No GUI Workbench / ui . / attach.json.

Validation

Did not run @all.

• python3 scripts/verify_agent_contract.py
• python3 scripts/refresh_agent_index.py --check
• python3 scripts/sync_consumer_guidance.py --check
• ./gradlew test
• ./gradlew publishToMavenLocal
• ./maven-consumer-project/mvnw -f maven-consumer-project/pom.xml -U test -Dpkb_runvars.pkb_browser=CHROME_HEADLESS -Dpkb_runvars.pkb_tags=@diagnostic-reporting