feat: recognize Fable/Mythos model families with 1M context window

Claude Fable 5 / Mythos 5 (claude-fable-5, claude-mythos-5) are not
matched by any built-in family, so the context window falls back to
the 200k default while these models ship with a 1M-token context
window by default (no [1m] suffix in the model ID to trigger the
context modifier).

Add fable/mythos built-in families with a 1_000_000 limit, reusing
the existing version-extraction regex (claude-fable-5 -> "Fable 5").

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: coocon

src/config/models.rs

@@ -102,6 +102,10 @@ impl ModelConfig {
                 BuiltinModelFamily::new("sonnet", "Sonnet", 200_000),
                 BuiltinModelFamily::new("opus", "Opus", 200_000),
                 BuiltinModelFamily::new("haiku", "Haiku", 200_000),
+                // Mythos-class models (Fable 5 / Mythos 5) ship with a 1M-token
+                // context window by default (no beta header / [1m] suffix required)
+                BuiltinModelFamily::new("fable", "Fable", 1_000_000),
+                BuiltinModelFamily::new("mythos", "Mythos", 1_000_000),
             ]
         })
     }
@@ -257,7 +261,7 @@ impl ModelConfig {
              # This file defines model display names and context limits for different LLM models\n\
              # File location: ~/.claude/ccline/models.toml\n\
              #\n\
-             # Claude models are automatically recognized (Sonnet, Opus, Haiku) with\n\
+             # Claude models are automatically recognized (Sonnet, Opus, Haiku, Fable, Mythos) with\n\
              # version extraction. You only need to add entries here for overrides or\n\
              # third-party models.\n\
              \n\
@@ -296,7 +300,7 @@ impl Default for ModelConfig {
     fn default() -> Self {
         Self {
             // Only third-party models need explicit entries.
-            // Claude models (Sonnet, Opus, Haiku) are handled by built-in regex families.
+            // Claude models (Sonnet, Opus, Haiku, Fable, Mythos) are handled by built-in regex families.
             model_entries: vec![
                 ModelEntry {
                     pattern: "glm-4.5".to_string(),