refactor(agent): remove reminder override plumbing

[aryasaatvik]

Summary

• remove agent.reminder from config schema and runtime types
• remove plan-agent default reminder injection path from agent registry
• stop session prompt reminder insertion from reading dynamic agent reminder overrides
• regenerate JS SDK v2 type surface to match removed reminder fields

Validation

• bun run typecheck
• bun turbo build --filter opencoder

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Exclude deprecated reminder key from option passthrough

Removing reminder from the knownKeys set means legacy configs like agent.plan.reminder are now treated as unknown fields and copied into options, which are later merged into model/provider request options in LLM.stream (packages/opencode/src/session/llm.ts). This changes a removed config knob into a live provider parameter and can cause request failures on strict providers (or at minimum leak obsolete config into runtime model options) for users who still have reminder in existing config files.

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