feat: initial model catalog with 196 models across 39 providers

Community-maintained TOML catalog for LibreFang. New models can be added
via PR without requiring a LibreFang binary release.

Includes validation script, bilingual docs, and GitHub templates.

providers/chatgpt.toml

@@ -0,0 +1,74 @@
+# ChatGPT (Session Auth / Codex Responses API) — https://chatgpt.com
+# Models: 5 (free with ChatGPT subscription via OAuth session)
+
+[provider]
+id = "chatgpt"
+display_name = "ChatGPT (Session Auth)"
+api_key_env = "CHATGPT_SESSION_TOKEN"
+base_url = "https://chatgpt.com/backend-api"
+key_required = true
+
+[[models]]
+id = "gpt-5.4-codex"
+display_name = "GPT-5.4 Codex"
+tier = "frontier"
+context_window = 200000
+max_output_tokens = 65536
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = ["chatgpt-5.4"]
+
+[[models]]
+id = "gpt-5.3-codex"
+display_name = "GPT-5.3 Codex"
+tier = "frontier"
+context_window = 200000
+max_output_tokens = 65536
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = ["chatgpt-5.3"]
+
+[[models]]
+id = "gpt-5.2-codex"
+display_name = "GPT-5.2 Codex"
+tier = "smart"
+context_window = 200000
+max_output_tokens = 65536
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = ["chatgpt-5.2"]
+
+[[models]]
+id = "gpt-5.1-codex"
+display_name = "GPT-5.1 Codex"
+tier = "smart"
+context_window = 200000
+max_output_tokens = 65536
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = ["chatgpt-5.1"]
+
+[[models]]
+id = "gpt-5.1-codex-mini"
+display_name = "GPT-5.1 Codex Mini"
+tier = "balanced"
+context_window = 200000
+max_output_tokens = 65536
+input_cost_per_m = 0.0
+output_cost_per_m = 0.0
+supports_tools = true
+supports_vision = false
+supports_streaming = true
+aliases = ["chatgpt-mini", "chatgpt"]