Metric 0.1.8

This release adds PostgreSQL as an independent storage backend and a minimal
interactive installer for Linux/macOS and Windows.

What's new

• Choose MongoDB or PostgreSQL, bundled with Metric or already running elsewhere.
• Enable the setup wizard explicitly; existing unattended installation commands
  and MongoDB defaults are preserved.
• Supply one visibly entered connection URI for an existing database. Configure
  native TCP or verified TLS and optional certificates for either backend.
• Keep one resource profile and editable TOML with persistent secrets and storage.
• Fresh Windows installations support PowerShell 5.1 and 7 while preserving the
  existing-data guard when installation secrets are missing.
• Shell installation through curl | sh isolates Docker commands from the
  script's standard input, preventing premature script consumption.
• Missed monitor runs use the configured retention period. A separate bounded
  background task corrects surviving older runs without postponing new checks.
• Component status reflects current worker lifetimes and database readiness;
  blob storage is shown as configured rather than unconditionally available.

Replay archiving remains unsupported. retention.replay_archive=true now fails
configuration validation. Existing held replay data is preserved; read the
upgrade instructions before changing this setting.

See Install Metric and Configuration.
PostgreSQL functional checks passed for the backend. The installer passed local
Docker checks for both scripts, both backends and both placements, terminal wizard
checks, and verified TLS with required client certificates and rejected invalid
CA/hostname/key cases. Native macOS execution has not been tested. PostgreSQL load/soak
testing remains deferred; published MongoDB performance figures do not apply to it.

Data and upgrades

MongoDB requires schema generation 22 exactly, including the forward migration
from generation 21 for metric archives. PostgreSQL requires generation 21 and
applies missing immutable migrations before becoming ready. Switching backends
does not move existing data. Preserve the database, BlobStore and HMAC/secrets
together; see Backup and restore and Update Metric.