docs(audit): fix Ingestion Paths count and Purpose conjunction wording

Code-review feedback on c334de0:
- Ingestion Paths intro said 'Three write paths' but the section has four
  subsections (site hot-path append + 3 central writers). Reword to 'Four
  paths feed the central AuditLog -- one site originator and three central
  writers'.
- Purpose: 'dashboards plus drilldowns plus filter queries' read awkwardly;
  switch to standard comma list.

docs/requirements/Component-AuditLog.md

@@ -5,7 +5,7 @@
 Provides a single, append-only, forensic + operational record of every
 integration action initiated by, or terminating in, a script — across outbound
 API, outbound DB, notifications, and inbound API. One row per lifecycle event,
-rich payloads, long retention, dashboards plus drilldowns plus filter queries,
+rich payloads, long retention, dashboards, drilldowns, and filter queries,
 answering both forensic questions ("did instance X send notification Y on date
 Z, with what body?") and operational ones ("which inbound caller is hammering
 us right now?").
@@ -143,8 +143,8 @@ guarantee.
 
 ## Ingestion Paths
 
-Three write paths converge on the central `AuditLog`, all idempotent on
-`EventId`.
+Four paths feed the central `AuditLog` — one site originator and three central
+writers — all idempotent on `EventId`.
 
 ### Site hot-path append (site-originated events)