DX-G01: Add Decision Explorer campaign board

[RicheyWorks]

Overall Classification: WARN

Campaign: Decision Explorer Architecture Bootstrap Campaign

Goal: DX-G01

Scope:

• Docs/test-only campaign board and campaign-system index entry.
• Focused documentation guard for the Decision Explorer campaign board.

Summary:

• Adds docs/agent/DECISION_EXPLORER_CAMPAIGN_BOARD.md as the repo-native board for DX-G01 through DX-G10.
• Registers the board from docs/agent/CAMPAIGN_SYSTEM_INDEX.md.
• Captures read-only and simulation-only boundaries, PR tracking columns, checkpoint rules, verification expectations, and closeout criteria.
• Adds AgentDecisionExplorerCampaignBoardDocumentationTest to guard the board and index link.
• Keeps future Decision Explorer implementation work planned, not complete.

Verification:

• mvn test "-Dtest=AgentDecisionExplorerCampaignBoardDocumentationTest" passed after tightening required boundary phrases.
• mvn test "-Dtest=AgentDecisionExplorerCampaignBoardDocumentationTest,NextLevelArchitectureSkeletonDocumentationTest,AgentCampaignSystemIndexDocumentationTest,AgentCampaignSystemArchitectureDocumentationTest,AdvancedReadmeAgentContractDocumentationTest" passed: 30 tests, 0 failures, 0 errors, 0 skipped.
• mvn -q test passed.
• mvn -q "-DskipTests" package passed.
• mvn -B package passed: 2,562 tests, 0 failures, 0 errors, 0 skipped.
• git diff --check passed.
• git diff --cached --check passed.
• git diff --check origin/main...HEAD passed.
• .\scripts\smoke\enterprise-lab-workflow.ps1 -Package passed.

Baseline note:

• PR Add next-level architecture skeleton #334 was merged at d435fffea92a28f39e85d830e803dcb3600dab32.
• GitHub reported no post-merge main push runs for that merge commit during local preparation.
• Do not claim DX-G01 complete until this PR is merged and post-merge main CI/CodeQL are green.

Safety:

• No production code changed.
• No Maven config changed.
• No CI/workflow changed.
• No Dockerfile/Compose changed.
• No scripts, runtime resources, endpoints, secrets, external targets, deployment, or automation changed.
• No later DX goal was started as a PR.

Not-proven boundaries:

• No production readiness/certification.
• No live-cloud or real-tenant validation.
• No benchmark/load/stress proof.
• No throughput/p95/p99 production evidence.
• No runtime Decision Explorer endpoint, UI, storage/export, replay, or evidence packet implementation.
• No broader automation.

[RicheyWorks]

Temporarily closing and reopening this same PR to refresh missing GitHub Actions check emission. No branch deletion and no scope change.