global-monitor: add clickhouse writer

[snormore]

Summary of Changes

• Add ClickHouse as a second telemetry backend alongside the existing InfluxDB writer, with both independently toggleable via environment variables
• Include goose-based migration setup with an initial migration creating 3 tables: solana_validator_icmp_probe, solana_validator_tpuquic_probe, doublezero_user_icmp_probe
• Introduce a ProbeWriter interface so planners can be tested without a real ClickHouse connection

Diff Breakdown

Category	Files	Lines (+/-)	Net
Core logic	7	+831 / -19	+812
Scaffolding	3	+274 / -0	+274
Tests	5	+510 / -12	+498
Config/build	2	+92 / -72	+20

~⅓ tests, ~½ core logic, remainder is migration scaffolding and dependency updates.

Key files (click to expand)

• telemetry/global-monitor/internal/clickhouse/writer.go — new buffered ClickHouse writer with typed row structs per table, batch insert flush, and ProbeWriter interface
• telemetry/global-monitor/db/clickhouse/migrations/20260404000001_init.sql — initial migration creating 3 MergeTree tables with monthly partitioning and 90-day TTL
• telemetry/global-monitor/internal/gm/planner_dz_icmp.go — add recordClickHouseRow() for DZ user ICMP probes including Solana cross-reference fields
• telemetry/global-monitor/internal/gm/planner_sol_tpuquic.go — add recordClickHouseRow() for Solana validator TPUQUIC probes
• telemetry/global-monitor/internal/gm/planner_sol_icmp.go — add recordClickHouseRow() for Solana validator ICMP probes
• telemetry/global-monitor/internal/clickhouse/migrations.go — goose migration runner adapted for slog
• telemetry/global-monitor/cmd/global-monitor/main.go — wire ClickHouse config via env vars, run migrations on startup, pass writer to runner
• telemetry/global-monitor/internal/gm/runner.go — add ClickHouseWriter to config, flush buffered rows at end of each tick

Testing Verification

• Unit tests added for all 3 planners verifying ClickHouse row recording: success case (all fields populated), failure case (probe_ok=false with fail reason), not-ready case (no row written), and nil writer safety
• Writer buffer tests: correct accumulation per table, concurrent append safety with 300 goroutines
• All existing InfluxDB recording tests continue to pass unchanged