Slash commands (/quit, /help) + zero compiler warnings

1. /quit and /help commands restored:
   - /quit: exits the interactive loop
   - /help: shows formatted help box with available commands & tips
   - Unknown commands get a friendly error pointing to /help
   - Slash commands intercepted before LLM processing (no token waste)

2. Zero warnings across entire workspace (13 files fixed):
   - Fixed ambiguous glob re-exports in gyandoot-core
   - Added #[allow(dead_code)] on intentional dead fields
   - Fixed unused imports, variables, and macros
   - Fixed unused assignments in subagents
   - cleaned up service.rs, profile, kanban warnings

install.sh now produces a completely clean build with zero warnings.

src/main.rs

@@ -303,8 +303,10 @@ fn load_and_convert_config(path: &std::path::Path) -> Result<gyandoot_core::conf
         model: String,
         temperature: Option<f64>,
         max_tokens: Option<u32>,
+        #[allow(dead_code)]
         #[serde(default)]
         merge_system: bool,
+        #[allow(dead_code)]
         #[serde(default)]
         no_tools: bool,
     }