feat: remote metrics HTTP reporter (spec 003) + cleanups

Summary

Implements spec 003 — remote metrics reporter: forward each metric/cycle event to a configurable remote monitoring server in parallel with the existing stdout JSON reporter. Also bundles a handful of quality-of-life improvements that came up while building it.

Commits

• feat(reporter) — new HttpReporter (infrastructure) + CompositeReporter (domain) fan events out to N reporters; wired through main.py, gated by REMOTE_REPORTER_ENABLED. Failures log but never block the next poll cycle.
• feat(config) — relax READ_INTERVAL_SECONDS validation from the hard == 30 invariant to > 0. Unblocks the existing config.toml value of 10. Default still 30.
• feat(metrics) — bump power and reactive_power rounding from 1 → 3 decimals (x.xxx), matching the DDS238-1-ZN's native 0.001 kW resolution.
• perf(tests) — replace subprocess.Popen in test_entrypoint_configuration.py with fork-based multiprocessing calls into main(). Full pytest suite drops 4.75s → ~1.0s (-78%) with identical coverage (signal delivery preserved via real child PID).
• docs(constitution) — bump constitution to v1.2.0: formalize Todoist task ID naming (`[T###] `), description, and full `Backlog → In progress → Done` lifecycle plus `Blocked - Waiting for` semantics. Mirrored in `tasks-template.md`.
• chore(config) — enable remote reporter and resolve hostname via `vandalsweb.internal`.
• chore(claude) — local Claude Code settings tweak.

Test plan

• `make py/pytest` — 110/110 pass in ~1.0s
• Smoke run inside container with `REMOTE_REPORTER_ENABLED=true` against a stubbed remote server; confirm `metric_read_succeeded` events POSTed.
• Verify `READ_INTERVAL_SECONDS=10` from `config.toml` no longer raises at startup.
• Confirm power readings in stdout JSON now show 3 decimals.

🤖 Generated with Claude Code