Add Time-of-Use tariff write to @teslemetry/api

[Bre77]

Intent

• The tier-2 parity audit (Homey/Node-RED vs the HA teslemetry integration) found one
  genuine client-library gap across the whole TypeScript ecosystem: Time-of-Use tariff write.
  Every other absent write in either wrapper already had a method on @teslemetry/api - this was
  the one that didn't, so no amount of wrapper work in Homey or Node-RED could close it.
  • Approach: add TeslemetryEnergyApi.setTimeOfUseSettings(), mirroring the server's
    POST /api/1/energy_sites/{id}/time_of_use_settings route schema (tou_settings.tariff_content_v2).
  • The generated OpenAPI client (src/client/sdk.gen.ts) already had the underlying
    postApi1EnergySitesByIdTimeOfUseSettings function from a prior spec sync - no codegen/spec
    change was needed, just a hand-written wrapper following the existing pass-through-body idiom
    used by neighboring methods like addChargeSchedule/setScheduledDeparture.
  • Typing: request body is typed via the generated PostApi1EnergySitesByIdTimeOfUseSettingsData["body"]
    (no any), consistent with how other complex-body setters in this file are typed.
• Scope boundary: library method only. Wiring this into homebridge-teslemetry,
  n8n-nodes-teslemetry, or iobroker.teslemetry is explicitly out of scope here - those are
  follow-up stories per the audit's recommendations.

What Changed

• packages/api/src/TeslemetryEnergyApi.ts: new setTimeOfUseSettings(body) method.
• packages/api/test/energyApi.test.ts: new test asserting the method POSTs the
  tou_settings body to the correct per-site URL and returns the parsed response.
• .changeset/tou-tariff-write.md: minor version bump changeset for @teslemetry/api.
• AGENTS.md: one-line note that the generated client often already has functions for
  endpoints the hand-written API classes haven't wrapped yet - worth checking before assuming
  an SDK gap needs a spec regen.

Risk Assessment

Low risk, additive-only change to the SDK. No existing methods or call sites touched.

Testing

• pnpm --filter @teslemetry/api test - all 8 tests pass (new test included)
• pnpm --filter @teslemetry/api tsc - clean
• pnpm lint (root, oxlint) - clean
• pnpm --filter @teslemetry/api build - clean

Full narrative / original brief

[E1.4] typescript-teslemetry: add the Time-of-Use (TOU) tariff WRITE capability to
@teslemetry/api (packages/api) - identified by the parity audit
(/home/brett/firstmate/data/e14-tier2-parity-m2/report.md) as the single true
client-library-level gap blocking tier-2 integrations from TOU control.

Scope:

1. Read the parity report's evidence for exactly which endpoint/shape is missing, and mirror
   the api server's route schema (the Teslemetry api repo cloned at
   /home/brett/firstmate/projects/api - the energy tariff routes and their request schemas are
   the source of truth; the ENERGY_TARIFF_OUTPUT shape in src/routes/mcp/ as secondary
   reference).
2. Implement in the library's existing idioms (neighboring energy-site methods for style,
   typing, and test patterns). Type the request per the server schema - no any-bags.
3. Tests per the package's conventions.
4. Library method only - do NOT wire it into the homebridge/n8n/iobroker packages in this PR
   (consumers are follow-up stories).