Add dynamic warm capacity target computation

[bill-ph]

Summary

• add K8s dynamic warm-capacity file/env config plumbing without public docs or CLI flags yet
• add configstore aggregation for recent warm-capacity miss buckets
• add pure image-scoped target computation from base targets plus recent no-idle misses
• clamp warm_capacity_demand_ttl to at least warm_capacity_miss_window
• treat shared_warm_target as the default image base target and keep pinned-image floors separate
• clear per-image warm targets during planned drain so warm spawning stops reliably

This intentionally keeps the PR C/D boundary: PR C computes bucket-derived targets and preserves max_workers=0 as unbounded; PR D will wire these effective targets into the janitor reconciler, remove the #597 in-memory counter path, and add the public README/example/usage docs plus CLI flags for the dynamic knobs.

Tests

• go test ./configresolve
• go test .
• go test ./controlplane
• go test ./cmd/duckgres-controlplane
• go test -tags kubernetes -run 'TestOrgRouterAdapterSetWarmCapacityTargetZeroClearsAllWarmTargets|TestOrgRouterReconcileWarmCapacity|TestComputeDynamicWarmCapacityTargets' ./controlplane
• go test -run 'TestRecordWarmCapacityMiss|TestListWarmCapacityMissesSince|TestPruneWarmCapacityMissBuckets' ./tests/configstore
• go test -tags kubernetes ./controlplane ./cmd/duckgres-controlplane
• go test ./... was run; it failed in existing tests/integration catalog compatibility test TestCatalogPsqlCommands/psql_dn because Duckgres returned 3 schema rows vs PostgreSQL's 2.