Drop unused ID Zod statics

[kitlangton]

Summary

• Remove unused .zod statics from simple session/workspace ID schemas.
• Convert TUI session ID validation to Effect Schema decoding.
• Update schema decoding tests to use Effect decoders for IDs without Zod statics.

Testing

• bun test --timeout 5000 test/session/schema-decoding.test.ts test/session/compaction.test.ts -t "summarizes only the head|anchors repeated compactions|keeps recent pre-compaction|ignores previous summaries|accepts minimal session"
• bun typecheck from packages/opencode
• bunx prettier --check packages/opencode/src/cli/cmd/tui/validate-session.ts packages/opencode/src/session/schema.ts packages/opencode/src/control-plane/schema.ts packages/opencode/test/session/schema-decoding.test.ts packages/opencode/test/session/compaction.test.ts
• bunx oxlint packages/opencode/src/cli/cmd/tui/validate-session.ts packages/opencode/src/control-plane/schema.ts packages/opencode/src/session/schema.ts packages/opencode/test/session/schema-decoding.test.ts

Stack

1. Migrate configurable compaction tests #26732
2. Migrate compaction LLM test #26733
3. Migrate LLM compaction tail tests #26734
4. Migrate compaction plugin test #26736
5. Migrate compaction tool-call test #26737
6. Replace compaction create test fixtures #26738
7. Drop compaction create facade #26739
8. Drop unused ID Zod statics #26740 👈 current
9. Simplify compaction test helpers #26742