feat(cmd): add side-aware targeting and trends telemetry

[igormf]

Summary

This is the follow-up feature PR requested in #30 after #24 landed.

It keeps the auth/runtime fixes that merged through #24 on main and layers the user-facing targeting improvements on top of the current codebase.

What Changed

• add side-aware targeting helpers so commands can address left, right, all, or an explicit household user
• make status report discovered household targeting mode, including split sides vs solo
• make on, off, and temp default to all discovered targets when no side/user is provided
• keep per-user control paths for households that expose individual users instead of simple side labels
• add timezone-aware trends/presence support and tests around the new targeting logic
• preserve the token cache/runtime compatibility needed for local Windows execution

UX Notes

Examples supported by this branch:

• eightctl status
• eightctl on
• eightctl off --side right
• eightctl temp -- -40
• eightctl temp --side left 20
• eightctl presence --from 2026-04-01 --to 2026-04-07

If the household is split, side names are surfaced. If the device is effectively single-zone, commands report solo and target the single available zone.

Verification

• go test ./...
• golangci-lint run ./...

Context

• requested split-out follow-up from closed PR Fix auth/runtime issues and add side-aware targeting #30
• based on current main after fix(client): use form-urlencoded for OAuth token endpoint #24, fix: update API calls for current Eight Sleep endpoints #31, docs: align README with removed metrics/schedule subcommands #32, fix(cmd): stop travel subcommands clobbering persistent viper keys #33, and fix(cmd): read --date/--from/--to from cobra flags instead of viper #34