insta db stats: connections x/y, active count, cache hit rate

[tonychang04]

New read-only command over GET /projects/:id/database/metrics (real values arrive with InsForge/insta-platform#175 + InsForge/insta-db#112):

$ insta db stats
postgres default (running)
  connections  5 / 100 (2 active)
  cache hit    99.2%
  size         7.6 MiB

• Suspended instance → (suspended) + structural zeros, never dialed (wake-safe).
• Unmeasured values (old platform, no cache traffic) print —, never a fake 0.
• --json, --branch, --group as usual; pure-seam dbStatsLines with tests (221 passed).

🤖 Generated with Claude Code

https://claude.ai/code/session_01PUxvcou8vdZCqPBcNS4BFe

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Summary by cubic

Add a read-only insta db stats command that shows Postgres connections total/max (with active count), cache hit rate, database size, and the Postgres server version in the header via GET /projects/:id/database/metrics. On insta-db-backed services it is wake-safe and shows "(suspended)"; others may wake; it supports --json, --branch, --group, and uses "—" for unmeasured values.

^{Written for commit 837dca7. Summary will update on new commits.}

[cursor]

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[jwfing]

LGTM - approved.