…yId)

…ngth + head test

…e-click

Double-clicking a clickhouse node did nothing because two node-type gates
omitted it: selectedNodeHasPrimaryEvaluateExpandTarget() fell through to
default:false (routing to the fallback dialog instead of the primary 1/n
path), and openPrimaryExpandDialogForSelectedNode() had no clickhouse branch
to open the first field. Add both, plus the clickhouse close in
closeAllExpressionExpandDialogs(), matching the bigquery/supabase pattern.

Honor user-entered limits exactly and emit no LIMIT clause when limit<=0,
matching the Supabase 0=fetch-all semantics. Updates the field label, DSL
prompt, and node doc accordingly.

clickhouse-connect returns datetime/Decimal/UUID/IP/bytes and nested
containers; node output is serialized with json.dumps downstream, which
raised 'Object of type datetime is not JSON serializable'. Normalize all
row values at the service boundary (datetime->ISO, Decimal->float,
UUID/IP->str, bytes->utf-8, recurse into Array/Tuple/Map).

Each operation created a fresh clickhouse-connect client (~5ms TCP+session
setup, measured 6.1ms cold vs 1.0ms warm). Add a process-wide client pool
keyed by connection (mirrors grist/qdrant/redis pools), wired into the
startup warm-up and shutdown close hooks.