CBG-5715: bound max_processes, mirror the _changes body defaults

max_processes is a uint, and db/event_manager.go:69-70 maps 0 to
kMaxActiveEvents (500), so document minimum: 0 with the effective
default and say what 0 means.  Raised by Copilot on #8654.

heartbeat and timeout in the _changes POST bodies now carry the same
defaults and bounds already documented on the GET query parameters:
heartbeat defaults to 0 and, when non-zero, is clamped up to
kMinHeartbeatMS (25000); timeout defaults to kDefaultTimeoutMS (300000)
and is capped at kMaxTimeoutMS (900000).  See GetRestrictedInt, which
readChangesOptionsFromJSON calls with allowZero=true.  Copilot flagged
these as heartbeat-only, but the timeout default is 300000, not 0.

Also drops the revs_limit allow_conflicts note.  Both branches it
describes exist (db/database.go:504-508, rest/config.go:936-940) but
neither is reachable from config: allow_conflicts=true is rejected in
the same validateVersion (rest/config.go:1149-1150) and
DefaultAllowConflicts is false, so only the test-only
EnableAllowConflicts gets there.  Raised by @factory-droid on #8656.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: torcolvin

docs/api/components/schemas.yaml

@@ -1274,8 +1274,10 @@ Database:
                       type: boolean
                       default: false
         max_processes:
-          description: The maximum amount of concurrent event handling independent functions that can be running at the same time.
+          description: The maximum amount of concurrent event handling independent functions that can be running at the same time. Setting to 0 uses the default.
           type: integer
+          default: 500
+          minimum: 0
         wait_for_process:
           description: The maximum amount of time (in milliseconds) to wait when the event queue is full.
           type: string
@@ -1613,8 +1615,6 @@ Database:
     revs_limit:
       description: |-
         The maximum depth a document's revision tree can grow to.
-
-        Defaults to 100 when `allow_conflicts` is enabled, and must be at least 20 in that case.
       type: integer
       default: 50
       minimum: 1

docs/api/paths/admin/keyspace-_changes.yaml

@@ -188,11 +188,15 @@ post:
               items:
                 type: string
             heartbeat:
-              description: The interval (in milliseconds) to send an empty line (CRLF) in the response. This is to help prevent gateways from deciding the socket is idle and therefore closing it. This is only applicable to `feed=longpoll` or `feed=continuous`. This will override any timeouts to keep the feed alive indefinitely. Setting to 0 results in no heartbeat. The maximum heartbeat can be set in the server replication configuration.
+              description: The interval (in milliseconds) to send an empty line (CRLF) in the response. This is to help prevent gateways from deciding the socket is idle and therefore closing it. This is only applicable to `feed=longpoll` or `feed=continuous`. This will override any timeouts to keep the feed alive indefinitely. Setting to 0 results in no heartbeat. The maximum heartbeat can be set in the server replication configuration. If heartbeat is non zero, it must be at least 25000 milliseconds.
               type: integer
+              default: 0
             timeout:
               description: 'This is the maximum period (in milliseconds) to wait for a change before the response is sent, even if there are no results. This is only applicable for `feed=longpoll` or `feed=continuous` changes feeds. Setting to 0 results in no timeout.'
               type: integer
+              default: 300000
+              maximum: 900000
+              minimum: 0
             feed:
               description: 'The type of changes feed to use. '
               type: string

docs/api/paths/public/keyspace-_changes.yaml

@@ -175,11 +175,15 @@ post:
               items:
                 type: string
             heartbeat:
-              description: The interval (in milliseconds) to send an empty line (CRLF) in the response. This is to help prevent gateways from deciding the socket is idle and therefore closing it. This is only applicable to `feed=longpoll` or `feed=continuous`. This will override any timeouts to keep the feed alive indefinitely. Setting to 0 results in no heartbeat. The maximum heartbeat can be set in the server replication configuration.
+              description: The interval (in milliseconds) to send an empty line (CRLF) in the response. This is to help prevent gateways from deciding the socket is idle and therefore closing it. This is only applicable to `feed=longpoll` or `feed=continuous`. This will override any timeouts to keep the feed alive indefinitely. Setting to 0 results in no heartbeat. The maximum heartbeat can be set in the server replication configuration. If heartbeat is non zero, it must be at least 25000 milliseconds.
               type: integer
+              default: 0
             timeout:
               description: 'This is the maximum period (in milliseconds) to wait for a change before the response is sent, even if there are no results. This is only applicable for `feed=longpoll` or `feed=continuous` changes feeds. Setting to 0 results in no timeout.'
               type: integer
+              default: 300000
+              maximum: 900000
+              minimum: 0
             feed:
               description: 'The type of changes feed to use. '
               type: string