feat(session): persist review and investigation provenance

[Patel230]

Summary

• Adds Kind, ReviewSkills, ReviewPrompt, InvestigateRunID, and InvestigateTopic fields to WriteCommittedOptions and CommittedMetadata, so committed checkpoints carry session-purpose context
• Wires provenance fields through both GitStore (v1) and V2GitStore write paths, and through ManualCommitStrategy.CondenseSession
• Adds KindAgentInvestigate session kind and Kind.IsInvestigation() alongside the existing KindAgentReview
• Adds applyProvenanceEnvToState in manual_commit_hooks_3.go to read env vars set by trace investigate and stamp the running session state
• Test helpers: SimulateUserPromptSubmitWithReviewEnvVars, TestEnv.WriteSettings, composeReviewPromptForTest; GitCheckoutBranch hardened with Force: true

Test plan

• go test ./cli/checkpoint/... ./cli/strategy/... ./cli/session/... passes
• go test ./cli/integration_test/... -race passes
• Commit a session with TRACE_REVIEW_SESSION=1 set and confirm CommittedMetadata.Kind == "agent_review" in the written JSON
• Commit a session with TRACE_INVESTIGATE_SESSION=1 set and confirm Kind == "agent_investigate" and InvestigateTopic is populated

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