Add proposal cards for new agent actions in chat timeline

[akgohain]

Motivation

• Render two new agent proposal types (prioritize_failure_hotspots, preview_correction_impact) as readable cards in the chat timeline to make action intent and key fields visible at a glance.
• Surface a compact rationale and a small set of important fields so reviewers can act quickly while preserving existing approve/reject workflows.

Description

• Add client/src/contexts/workflow/proposalCardConfig.js which defines card metadata for the two new proposal types and provides getProposalCardConfig and buildProposalSummary helpers.
• Add client/src/components/chat/AgentProposalCard.js which renders title/description, a truncated rationale, key fields from the config, and Approve/Reject buttons; it uses a data-testid for testability.
• Add client/src/components/chat/renderAgentTimelineItem.js which branches on message.kind === "proposal" and renders the AgentProposalCard, otherwise returning the plain message content.
• Add tests at client/src/__tests__/agentProposalCards.test.js that validate rendering of both new proposal card types, that key fields and compact rationale appear, that Approve/Reject buttons call handlers, and that non-proposal timeline rendering is unchanged.

Testing

• Running cd client && npx react-scripts test --watchAll=false --runInBand agentProposalCards passed with 1 test suite and 3 tests all green.
• Running npm --prefix client run build produced a successful production build (with unrelated lint warnings) and the build output was created.
• Running npm --prefix client test -- --watchAll=false --runInBand agentProposalCards failed because the top-level client/package.json does not provide a test script, so tests were executed with npx react-scripts test instead.

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Codex Task

[akgohain]

Consolidated into draft PR #165 (feat/codex-wave-integration). Closing this source draft to keep review in one place.