feat: implement tweaks plan - modals, smart shell, spinner, /models, debug log, skills

Phase 1: Permission modal dialog, session resume modal, HistoryInput with
up/down arrow cycling, remove "You:" echo from chat log, LLM client cleanup
on unmount.

Phase 2: Smart shell auto-approve using allowed/denied command lists from
ToolsConfig, animated thinking spinner with live token count in status bar.

Phase 3: /models slash command (list + switch), CLI directory positional
argument, JSONL debug logger with rotation.

Phase 4: Skills system with SkillsManager, load_skill LLM tool, /skills
listing, skill invocation via slash commands, system prompt integration.

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

app/models/config.py

@@ -90,6 +90,24 @@ class DisplayConfig(BaseModel):
     stream_output: bool = Field(default=True, description="Stream LLM output to terminal")
 
 
+class SkillsConfig(BaseModel):
+    """Skills system configuration."""
+
+    enabled: bool = Field(default=True, description="Enable skills system")
+    directories: list[Path] = Field(
+        default_factory=lambda: [Path(".sneakycode/skills")],
+        description="Directories to scan for skill markdown files",
+    )
+
+
+class DebugConfig(BaseModel):
+    """Debug logging configuration."""
+
+    enabled: bool = Field(default=False, description="Enable debug logging")
+    log_dir: Path = Field(default=Path(".sneakycode/logs"), description="Debug log directory")
+    max_files: int = Field(default=10, description="Max debug log files to retain")
+
+
 class AppConfig(BaseModel):
     """Top-level application configuration composing all sub-configs."""
 
@@ -99,6 +117,8 @@ class AppConfig(BaseModel):
     tools: ToolsConfig = Field(default_factory=ToolsConfig)
     display: DisplayConfig = Field(default_factory=DisplayConfig)
     session: SessionConfig = Field(default_factory=SessionConfig)
+    debug: DebugConfig = Field(default_factory=DebugConfig)
+    skills: SkillsConfig = Field(default_factory=SkillsConfig)
 
     @model_validator(mode="after")
     def resolve_workspace_root(self) -> "AppConfig":