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>

dev/example.cfg

@@ -0,0 +1,17 @@
+# Example node configuration.
+# All keys are optional — missing keys use schema defaults.
+
+[node]
+name         = v4l2:microscope
+site_id      = 0
+tcp_port     = 8001
+function     = source
+
+[discovery]
+interval_ms       = 5000
+timeout_intervals = 3
+connect_mask      = relay, controller   ; auto-connect to relays and controllers
+
+[transport]
+max_connections = 16
+max_payload     = 16777216   ; 16 MB