Revert fresh-agent progressive hydration

[danshapiro]

Summary

• Reverts only d9bdc21 / PR Fresh-agent progressive hydration #468, Fresh-agent progressive hydration.
• Preserves later unrelated work from PR Fix thinking text color in serif transcript style #467 and PR Refactor settings UI tabs #469.
• Restores the previous FreshOpenCode history reader path and removes restart-time progressive hydration changes that caused client rehydration payload/request fan-out.

Verification

• Pre-worktree base check: npm test on main/origin/main passed.
• npm run typecheck passed.
• Focused client/shared fresh-agent tests passed: 8 files, 398 tests.
• Focused server fresh-agent tests passed: 12 files, 161 tests.
• Full coordinated npm run check passed across client/default, server, and electron stages.

Safety

• No deployment.
• No self-hosted Freshell server restart.
• No live host mutation.
• No production dist overwrite.