feat(miner-foundation): extract reward-risk scoring into gittensory-engine

[JSONbored]

Move src/signals/reward-risk.ts (877 lines) into packages/gittensory-engine/src/reward-risk.ts — the deterministic reward/risk reasoning signals a miner needs to rank candidate work locally (mirroring what the maintainer-side gate already computes). Given its size, keep this a pure lift-and-shift with no behavior changes; if any internal dependency does not yet have an engine-side home, port that minimal dependency alongside it in this same issue rather than reaching back into src/.

Deliverables

• packages/gittensory-engine/src/reward-risk.ts — verbatim port of the full module.
• src/signals/reward-risk.ts becomes a thin re-export shim from @jsonbored/gittensory-engine preserving every existing export name.
• The full existing reward-risk test suite passes unmodified against the shim.
• packages/gittensory-engine/src/index.ts re-exports the new module.
• If the module's line count plus its minimal direct dependencies would exceed the 1000-LOC issue cap, split into a follow-up issue for the dependency and note that split explicitly in the PR description (do not silently under-deliver).

References

• src/signals/reward-risk.ts (877 lines, full file) — the module to port.
• packages/gittensory-engine/ — created by the package-skeleton issue (must land first).

[linear-code]

JSO-2378