feat(tamanu): expected-services model + robust pm2 discovery on Windows

[passcod]

Summary

Replaces the doctor's tamanu_service healthcheck with a declarative
expected-services model and adds a robust pm2 discovery path for Windows.

Expected-services model

• New tamanu::services module: Supervisor, ServerKind (from ApiServerKind), Expectation, Instances (Single / NumericAtLeast(n) / Named(&[…])), ExpectedState (Up/Down), plus an expected(supervisor, kind, &config) function.
• Encodes the current ruleset: tasks singleton; frontend@a/@b and forbidden tamanu-facility singleton on systemd; api ≥2; Central fhir-resolve/fhir-refresh when fhir.worker.enabled; Facility sync singleton.
• New fhir.worker.enabled field on TamanuConfig.

Doctor check

• Discovers tamanu-* units/processes, matches each expectation, diagnoses missing / shortfall / forbidden / not-running. Unrelated tamanu-* services are recorded as informational extras rather than counted against the check.
• Probes systemctl is-enabled for any forbidden unit that didn't show up loaded.
• Exposes structured details: per-expectation outcome, raw services, extras, and (for pm2) the discovery source.

pm2 discovery on Windows

• New tamanu::pm2 module. The doctor no longer calls Command::new("pm2") directly.
• CLI lookup tries BESTOOL_PM2_COMMAND, then pm2.cmd/pm2.bat, then common npm-global install paths and C:\pm2\pm2.cmd.
• If the CLI isn't reachable, falls back to reading PM2_HOME/dump.pm2 directly and checking PM2_HOME/pids/<name>-<id>.pid against the OS process list (via sysinfo). Candidate PM2_HOME locations: env var, C:\pm2, ~/.pm2.
• Source (cli / dump) surfaces in the check details.

Tests cover the expected() matrix, the matching logic with synthetic discovered lists, and pm2 dump+pid parsing with tempdir fixtures.