Backend: Added optional `environment` query parameter to catalog,
search, stats, timeseries, punchcard, top-errors, logs, and agents
endpoints. ClickHouse queries filter by environment when specified
(literal SQL for AggregatingMergeTree, ? binds for raw tables).
StatsStore interface methods all accept environment parameter.
UI: Added EnvironmentSelector component (compact native select).
LayoutShell extracts distinct environments from agent data and
passes selected environment to catalog and agent queries via URL
search param (?env=). TopBar shows current environment label.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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