feat(scriptit): add native server and session integration patches

[noamzbr]

What

Six Script.it integration patches, one commit each, above OpenCode v2 + the carried upstream Stop PR.

Base: noam/v2-stop-base = v2 eb052f70 + dd5f3d12, the port of anomalyco/opencode#46721. This PR contains only the product changes above that base.

1. Managed server entrypoint: scriptit-serve uses explicit configuration, loopback authentication, stdin-owned lifetime and an in-process route to the upstream v1 converter.
2. Interactive turn completion: honor metadata.endTurn before requesting another model round, including incomplete-stream retries.
3. Shell identity/environment: derive user-shell message identity before creation, expose caller metadata to shell hooks and pass request-only environment without persisting it.
4. Tool refusals: map rejected Promise execute.before hooks to typed tool errors.
5. Settled Stop: wait for the shell's job before acknowledging Stop, so immediate session interruption cannot delete its result/capture.
6. Bounded shell history: persist a 16 KiB head + 48 KiB tail excerpt instead of the first 1 MiB.

Validation

• The six commits reconstruct all 32 files of the tested product patch exactly; no behavior change from splitting the commits.
• Generated protocol, OpenAPI and client output regenerated and matched the captured source.
• bun run check passes (lint and all 35 typecheck tasks).
• Bun 1.4.2: CLI wrapper test passes; server HTTP suite passes (12 tests).
• Core runner/step/session-shell/session-owned/plugin-failure/tool-shell suites: 339 pass, 19 skip, 6 fail. All six shell-approval failures also reproduce on noam/v2-stop-base; they are not introduced by these product patches. They assert Effect Exit object's internal shape in conditional/compound-shell approval cases.

Generated OpenCode client/API/OpenAPI output and the lockfile are excluded from the guided review and handwritten line counts.

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