docs: escape angle brackets in conf.c and fix page_core_api references

- conf.c: escape <key>, <value>, <action> placeholders in doc comment
- context.h, permission.h: fix \ref page_core_api to \ref api_pw_core

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pipewire/conf.c

@@ -1286,13 +1286,13 @@ int pw_conf_load_conf_for_context(struct pw_properties *props, struct pw_propert
  *             # actions are emitted.
  *             {
  *                 # all keys must match the value. ! negates. ~ starts regex.
- *                 <key> = <value>
+ *                 \<key\> = \<value\>
  *                 ...
  *             }
  *             ...
  *         ]
  *         actions = {
- *             <action> = <value>
+ *             \<action\> = \<value\>
  *             ...
  *         }
  *     }

src/pipewire/context.h

@@ -29,7 +29,7 @@ extern "C" {
  *    clients.
  *
  *  - Connect to another PipeWire instance (the main daemon, for
- *    example) and interact with it (See \ref page_core_api).
+ *    example) and interact with it (See \ref api_pw_core).
  *
  *  - Export a local implementation of an object to another
  *    instance.

src/pipewire/permission.h

@@ -16,7 +16,7 @@ extern "C" {
  * Permissions are kept for a client and describe what the client is
  * allowed to do with an object.
  *
- * See \ref page_core_api
+ * See \ref api_pw_core
  */
 
 /**