Add config module: INI loader with schema-driven defaults

Config_Def schema tables declare section/key/type/default per module.
Typed getters: config_get_str, _u16, _u32, _flags.
FLAGS type parses space/comma-separated tokens via a Config_Flag_Def table.
config_defaults() gives schema defaults without a file.
config_dump() prints effective values for diagnostics.

config_cli: load a file or --defaults and dump effective config.
dev/example.cfg: sample config covering node, discovery, transport.

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

include/config.h

@@ -0,0 +1,76 @@
+#pragma once
+
+#include <stdint.h>
+#include "error.h"
+
+/*
+ * INI-style config file loader with schema-driven defaults and validation.
+ *
+ * File format:
+ *   [section]
+ *   key = value    ; inline comments with ; or #
+ *   key = value    # same
+ *
+ * Whitespace around keys and values is stripped.
+ * Commas in values are treated as whitespace (useful for flag lists).
+ */
+
+typedef enum Config_Type {
+	CONFIG_STRING,   /* arbitrary string value                              */
+	CONFIG_UINT16,   /* decimal integer, fits u16                           */
+	CONFIG_UINT32,   /* decimal integer, fits u32                           */
+	CONFIG_FLAGS,    /* space/comma-separated tokens mapped via a flag table */
+} Config_Type;
+
+/*
+ * One entry in a flags table — maps a token string to a bitmask value.
+ * The table must be terminated by an entry with token = NULL.
+ */
+struct Config_Flag_Def {
+	const char *token;
+	uint32_t    value;
+};
+
+/*
+ * One entry in a config schema.
+ * Provide a table of these terminated by an entry with section = NULL.
+ */
+struct Config_Def {
+	const char              *section;
+	const char              *key;
+	Config_Type              type;
+	const char              *default_val;  /* string form of the default      */
+	const struct Config_Flag_Def *flags;   /* required when type = CONFIG_FLAGS */
+};
+
+struct Config;
+
+/*
+ * Load a config file and validate it against the schema.
+ * Keys present in the file but absent from the schema are ignored.
+ * Keys absent from the file are filled with their schema default.
+ */
+struct App_Error  config_load(struct Config **out,
+	const char            *path,
+	const struct Config_Def *schema);
+
+/*
+ * Load defaults only (no file). Useful when no config file is present
+ * but you still want schema-driven defaults.
+ */
+struct App_Error  config_defaults(struct Config **out,
+	const struct Config_Def *schema);
+
+void  config_free(struct Config *cfg);
+
+/*
+ * Typed getters. Return the effective value (file value or default).
+ * Caller must not free the returned string — it is owned by the Config.
+ */
+const char  *config_get_str  (struct Config *cfg, const char *section, const char *key);
+uint16_t     config_get_u16  (struct Config *cfg, const char *section, const char *key);
+uint32_t     config_get_u32  (struct Config *cfg, const char *section, const char *key);
+uint32_t     config_get_flags(struct Config *cfg, const char *section, const char *key);
+
+/* Print all effective key/value pairs to stdout — useful for diagnostics. */
+void  config_dump(struct Config *cfg);