docs(engine): document the Rent-a-Loop pipeline modules (idea-intake, loop-progress, results-payload)

[JSONbored]

Context

packages/loopover-engine/README.md documents most of the package's public API in per-module sections (## Objective-anchor calibration, ## Pairwise calibration, ## Plan DAG status helpers, etc.), each with a short explanation and a usage snippet. Three fully-implemented, already-exported, already-tested pure modules — the customer-facing spine of the Rent-a-Loop pipeline (epic #4778) — have zero README coverage:

• src/idea-intake.ts (issue Idea-intake bridge schema #4779, closed) — turns a freeform renter idea into a strict, claimable task-graph and scores it against the shared feasibility gate. Exports IdeaSubmission, AcceptanceCriterion, and the intake-validation/decomposition surface. Has solid module + per-export TSDoc already.
• src/loop-progress.ts (issue Real-time progress streaming #4800, closed) — builds the customer-facing progress snapshot from already-computed loop state, and decides when a snapshot changed enough to push. Exports LoopPhase, LoopRunStatus, ProgressSnapshot, MAX_PROGRESS_ACTIVITY, and the snapshot builder.
• src/results-payload.ts (issue Results delivery #4801, closed) — packages a completed loop iteration into the customer-facing result (PR link, plain-language summary, bounded diff preview). Exports IterationResult, ResultsPayload, MAX_DIFF_PREVIEW_FILES, and the composer function.

All three are re-exported through the package barrel (src/index.ts), all three ship with their own test/*.test.ts file, and all three already carry good inline TSDoc — this is purely a missing README narrative, not a missing-JSDoc problem. Confirmed via grep -ic over the current README: zero matches for idea-intake, loop-progress, or results-payload in any form.

Together these three form one coherent pipeline (idea → running loop → delivered result) that a reader of the README currently has no way to discover exists, even though opportunity-ranker, objective-anchor, and half a dozen calibration modules from the same package each get their own documented section.

Requirements

• Add one new ## section to packages/loopover-engine/README.md (or three short subsections under one umbrella heading) covering idea-intake.ts, loop-progress.ts, and results-payload.ts, in the same style as the existing "Plan DAG status helpers" / "Metadata opportunity signals" sections: a short explanation of what each module does, its key exported types, and one runnable usage snippet per module.
• Note explicitly (mirroring the modules' own header comments) that all three are pure, side-effect-free transforms — no IO, no network — since that's a load-bearing property of the package's design that the README already emphasizes for other modules (e.g. objective-anchor's "no model call, network call, wall-clock read, or random input").

Deliverables

• New README section(s) documenting idea-intake.ts, loop-progress.ts, results-payload.ts with exported types and a usage snippet each

Test Coverage Requirements

Docs-only change to packages/loopover-engine/README.md — outside coverage.include (Codecov collects coverage over src/** and packages/loopover-engine/src/**/packages/loopover-miner/lib/**, not *.md files). No Codecov gate applies; verify instead by making sure every code snippet in the new section actually type-checks/runs against the current exports (e.g. paste it into a scratch .ts file against the built package).

Expected Outcome

A reader of packages/loopover-engine/README.md can discover and use idea-intake.ts, loop-progress.ts, and results-payload.ts the same way they already can for the package's other pure modules, without having to read the source directly.

Links & Resources

• packages/loopover-engine/src/idea-intake.ts, src/loop-progress.ts, src/results-payload.ts
• packages/loopover-engine/test/ — existing tests for reference when writing usage snippets
• Closed issues Idea-intake bridge schema #4779, Real-time progress streaming #4800, Results delivery #4801 (the implementation issues), part of epic Epic: Miner Wave 5 — Rent-a-Loop #4778

[linear-code]

JSO-3997