cli: insta metrics + insta logs (observability)

[jwfing]

insta metrics <db|compute> [group] and insta logs <db|compute> [group] proxy the platform's
/metrics and /logs endpoints. Compute shows real series/lines; db surfaces the provider-limitation note.

Verified end-to-end against the platform dev:fake server (metrics compute → cpu/mem/req series; logs compute → lines; db → note).

🤖 Generated with Claude Code

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Summary by cubic

Adds observability to the CLI with insta metrics and insta logs, proxying the platform /metrics and /logs. Compute returns live series and log lines; DB shows a provider-limitation note.

• New Features
  • insta metrics <db|compute> [group]: fetches series with optional --branch --from --to --step; prints latest values or --json.
  • insta logs <db|compute> [group]: fetches lines with optional --branch --limit --region --instance; prints lines or --json.
  • Defaults branch to the linked project, shows notes for DB limits, and updates CLI wiring and README.

^{Written for commit 50fc2e4. Summary will update on new commits.}

[Fermionic-Lyu]

LGTM, Approved.