feat(planner): default stable releases to Energyplan

[frahlg]

Problem

config.Planner.EngineForBuild chose Energyplan only when the version matched vX.Y.Z-beta.N. A stable build (vX.Y.Z) with no planner.engine fell back to Core DP. Every beta tester runs Energyplan by default, so promoting a beta to the first native stable would switch each of them to another planner without notice. The home box has no explicit engine and would have switched.

Decision

The owner chose on 2026-10-07: stable uses Energyplan by default, the same as beta. Core DP still runs as the bounded shadow and fallback, Core still validates every plan, and planner.engine: core still selects Core DP.

Change

• planner_engine.go: match release tags with or without -beta.N. Development builds (v0.X.Y-dev.<hash>, dev), release candidates and non-Linux or 32-bit hosts keep Core.
• Tests: stable on linux/arm64 and amd64 gives Energyplan, stable on darwin gives Core, an explicit core on stable gives Core, and a dev-hash build gives Core. The batteryless admission test now expects Energyplan for the stable default on supported hosts.
• The help text in Settings → Planner, config.example.yaml and docs/architecture.md now say beta and stable.

The forecast pipeline was already the same for every channel (energyplanSupported only), so nothing else needed to change.

Tests

go test ./internal/config -run TestPlannerEngineForBuild, and go test ./cmd/ftw -run 'TestEnergyplanReleaseSelection|TestBuildMPC…' pass on macOS. The bundled-worker wiring test skips on macOS and runs in Linux CI. go vet is clean.

Open PRs #1051 and #1292 touch other sections of docs/architecture.md, and #1003 touches another section of config.example.yaml. This PR edits only the planner lines.

Release

This goes in the same beta as #1528, and that beta is the stable candidate.

🤖 Generated with Claude Code

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-07T11:35:29.049497Z	9be07c3	PR opened

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Reviewed commit: 9be07c3330

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Update the remaining docs for the stable default

This stable-default change leaves go/internal/config/config.go:693 saying an unset engine uses Energyplan only in betas, while optimizer/native/README.md:53-56 still explicitly says stable builds default to Core. Maintainers following either description can unintentionally select Energyplan on a stable Linux installation, so both references should be updated with the other documentation in this commit.

AGENTS.md reference: AGENTS.md:L274-L275

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