security: add per-client stream limit in PulseAudio protocol

There was no limit on the number of streams a single client could
create. Each stream allocates a 4MB ring buffer, allowing a malicious
client to exhaust server memory. Add a configurable pulse.max-streams
property (default 64) to limit streams per client.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/module-protocol-pulse.c

@@ -76,6 +76,7 @@
  *     #pulse.default.format   = F32
  *     #pulse.default.position = [ FL FR ]
  *     #pulse.idle.timeout     = 0
+ *     #pulse.max-streams      = 64
  * }
  *
  * pulse.properties.rules = [
@@ -247,6 +248,12 @@
  * save battery power. When the client resumes, it will unpause again.
  * A value of 0 disables this feature.
  *
+ *\code{.unparsed}
+ *     pulse.max-streams = 64
+ *\endcode
+ *
+ * The maximum number of streams a single client can create. Default is 64.
+ *
  * ## Command execution
  *
  * As part of the server startup sequence, a set of commands can be executed.