server: add presets (config) when using multiple models (#17859)

* llama-server: recursive GGUF loading

Replace flat directory scan with recursive traversal using
std::filesystem::recursive_directory_iterator. Support for
nested vendor/model layouts (e.g. vendor/model/*.gguf).
Model name now reflects the relative path within --models-dir
instead of just the filename. Aggregate files by parent
directory via std::map before constructing local_model

* server : router config POC (INI-based per-model settings)

* server: address review feedback from @aldehir and @ngxson

PEG parser usage improvements:
- Simplify parser instantiation (remove arena indirection)
- Optimize grammar usage (ws instead of zero_or_more, remove optional wrapping)
- Fix last line without newline bug (+ operator instead of <<)
- Remove redundant end position check

Feature scope:
- Remove auto-reload feature (will be separate PR per @ngxson)
- Keep config.ini auto-creation and template generation
- Preserve per-model customization logic

Co-authored-by: aldehir <aldehir@users.noreply.github.com>
Co-authored-by: ngxson <ngxson@users.noreply.github.com>

* server: adopt aldehir's line-oriented PEG parser

Complete rewrite of INI parser grammar and visitor:
- Use p.chars(), p.negate(), p.any() instead of p.until()
- Support end-of-line comments (key=value # comment)
- Handle EOF without trailing newline correctly
- Strict identifier validation ([a-zA-Z_][a-zA-Z0-9_.-]*)
- Simplified visitor (no pending state, no trim needed)
- Grammar handles whitespace natively via eol rule

Business validation preserved:
- Reject section names starting with LLAMA_ARG_*
- Accept only keys starting with LLAMA_ARG_*
- Require explicit section before key-value pairs

Co-authored-by: aldehir <aldehir@users.noreply.github.com>

* server: fix CLI/env duplication in child processes

Children now receive minimal CLI args (executable, model, port, alias)
instead of inheriting all router args. Global settings pass through
LLAMA_ARG_* environment variables only, eliminating duplicate config
warnings.

Fixes: Router args like -ngl, -fa were passed both via CLI and env,
causing 'will be overwritten' warnings on every child spawn

* add common/preset.cpp

* fix compile

* cont

* allow custom-path models

* add falsey check

* server: fix router model discovery and child process spawning

- Sanitize model names: replace / and \ with _ for display
- Recursive directory scan with relative path storage
- Convert relative paths to absolute when spawning children
- Filter router control args from child processes
- Refresh args after port assignment for correct port value
- Fallback preset lookup for compatibility
- Fix missing argv[0]: store server binary path before base_args parsing

* Revert "server: fix router model discovery and child process spawning"

This reverts commit e3832b42eeea7fcb108995966c7584479f745857.

* clarify about "no-" prefix

* correct render_args() to include binary path

* also remove arg LLAMA_ARG_MODELS_PRESET for child

* add co-author for ini parser code

Co-authored-by: aldehir <hello@alde.dev>

* also set LLAMA_ARG_HOST

* add CHILD_ADDR

* Remove dead code

---------

Co-authored-by: aldehir <aldehir@users.noreply.github.com>
Co-authored-by: ngxson <ngxson@users.noreply.github.com>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>
Co-authored-by: aldehir <hello@alde.dev>

common/arg.h

@@ -3,8 +3,10 @@
 #include "common.h"
 
 #include <set>
+#include <map>
 #include <string>
 #include <vector>
+#include <cstring>
 
 //
 // CLI argument parsing
@@ -24,6 +26,8 @@ struct common_arg {
     void (*handler_str_str)(common_params & params, const std::string &, const std::string &) = nullptr;
     void (*handler_int)    (common_params & params, int) = nullptr;
 
+    common_arg() = default;
+
     common_arg(
         const std::initializer_list<const char *> & args,
         const char * value_hint,
@@ -61,9 +65,29 @@ struct common_arg {
     bool is_exclude(enum llama_example ex);
     bool get_value_from_env(std::string & output) const;
     bool has_value_from_env() const;
-    std::string to_string();
+    std::string to_string() const;
+
+    // for using as key in std::map
+    bool operator<(const common_arg& other) const {
+        if (args.empty() || other.args.empty()) {
+            return false;
+        }
+        return strcmp(args[0], other.args[0]) < 0;
+    }
+    bool operator==(const common_arg& other) const {
+        if (args.empty() || other.args.empty()) {
+            return false;
+        }
+        return strcmp(args[0], other.args[0]) == 0;
+    }
 };
 
+namespace common_arg_utils {
+    bool is_truthy(const std::string & value);
+    bool is_falsey(const std::string & value);
+    bool is_autoy(const std::string & value);
+}
+
 struct common_params_context {
     enum llama_example ex = LLAMA_EXAMPLE_COMMON;
     common_params & params;
@@ -76,7 +100,11 @@ struct common_params_context {
 // if one argument has invalid value, it will automatically display usage of the specific argument (and not the full usage message)
 bool common_params_parse(int argc, char ** argv, common_params & params, llama_example ex, void(*print_usage)(int, char **) = nullptr);
 
-// function to be used by test-arg-parser
+// parse input arguments from CLI into a map
+// TODO: support repeated args in the future
+bool common_params_parse(int argc, char ** argv, llama_example ex, std::map<common_arg, std::string> & out_map);
+
+// initialize argument parser context - used by test-arg-parser and preset
 common_params_context common_params_parser_init(common_params & params, llama_example ex, void(*print_usage)(int, char **) = nullptr);
 
 struct common_remote_params {