Build operator observability dashboard and telemetry

[sam2tom]

Summary

• Add a compact operator overview with token, active Sandbox, measured CPU/memory, and node totals while retaining the four existing Runtime curves.
• Add request, terminal Turn, tool attempt, collector, node, and Core service tables. Unknown model attempts remain explicitly unavailable.
• Store bounded observability projections under consistent observability_* names and expose a deployment-admin read endpoint through AdminClient.

Data and safety

• API request metrics use completed responses and bounded route families; incomplete heartbeat coverage or recorded collector loss makes range rate, error rate, and p95 unavailable.
• Tool attempts are recorded only after journal persistence. Terminal Turn metrics come from durable timestamps. Node and Core service reads stay within the selected local console source.
• The migration renames runtime_history_samples to observability_runtime_samples in place and adds four bounded telemetry tables. No response, routing, or billing semantics change.

Validation

• make check against a task-specific PostgreSQL test database: Go/API/SQL, Web unit tests (75 files), Web build, and Playwright (148/148) passed. The final macOS Rust executor step cannot compile Linux-only rustix APIs; executor files are unchanged from main, and Linux CI is required for that gate.
• Focused Playwright rerun for operator tables and unpaired-console behavior: 2/2 passed.
• Web typecheck and request coverage unit test passed.
• Independent blind review completed; its two final findings were fixed.

Test-host deployment preflight

The Docker test host is still on bd597296, with 17 historical Sessions, 3 unreleased Runtime allocations, and a legacy static-key file. Current main removes static business keys and does not backfill historical ownership. Do not activate this revision over that database without an explicit data-transition decision. The existing release remains untouched while CI and that decision are pending.

[sam2tom]

Superseded by #96 per the updated product direction. The Dashboard observability redesign in this PR is being retired; future Console work will follow #96.