Add Boolean param kind that is always present true/false (ticket 018)

MetricPrimitiveKind gains Boolean, serialized as "boolean". A param
declared with kind Boolean skips capture-group validation and, instead
of being omitted when message_match_regex doesn't match, is present on
every log line as true/false based purely on whether the regex matches
(case-insensitively or per the regex's own flags). Params.tsx lets you
pick boolean as a kind and disables the now-unused capture group input.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/lib/api.ts

@@ -4,11 +4,13 @@ export type MetricPrimitive =
   | { Number: { Int: number } | { Float: number } }
   | { Timestamp: number }
   | { Duration: number }
+  | { Boolean: boolean }
 
 export function metricPrimitiveToDisplayString(value: MetricPrimitive): string {
   if ('String' in value) return value.String
   if ('Timestamp' in value) return String(value.Timestamp)
   if ('Duration' in value) return `${value.Duration}ms`
+  if ('Boolean' in value) return String(value.Boolean)
   if ('Int' in value.Number) return String(value.Number.Int)
   return String(value.Number.Float)
 }
@@ -25,7 +27,7 @@ export interface ParamDeclaration {
   name: string
   message_match_regex: string
   capture_group: string
-  kind: 'string' | 'number' | 'timestamp' | 'duration'
+  kind: 'string' | 'number' | 'timestamp' | 'duration' | 'boolean'
 }
 
 export interface TimelineBucket {