refactor: extract Goal prompt and report runtimes

[ByBrawe]

Summary

Continue the Loop source modularization by splitting Goal presentation responsibilities out of runtime/goal-runtime.js.

• add runtime/goal-prompt.js for persistent Goal prompt construction and file/context rendering;
• add runtime/goal-report.js for report path/text/write behavior;
• keep goal-runtime.js focused on Goal selection, evidence/progress helpers, and lifecycle mutations;
• preserve the existing public source surface by re-exporting buildGoalPrompt, goalReportPath, goalReportText, and writeGoalReport from goal-runtime.js, so current consumers/tests do not need a compatibility migration;
• syntax-gate the new source modules while retaining the existing Goal runtime regression suite.

Behavior-preserving source modularization only. No runtime state schema or user-visible command behavior change. The committed single-file bundle is intentionally not changed in this source-only slice; the Bundle Gate regenerated and exercised the exact source head on Linux and Windows.

Verification

Exact head 2584da1a10e15df67b5690c08b7c817905b14ad4:

• CI: success on Linux/Windows, OpenCode 1.4.0/latest compatibility, and real OpenCode Loop hosts;
• Single-file Bundle Gate: success on Linux/Windows, including source regeneration, generated-entry import, real-host Loop/queued-Goal canaries, and generated-bundle regression suite;
• V2 Lifecycle Contract: success.

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