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.

crates/gyandoot-agent/src/tools.rs

@@ -58,6 +58,7 @@ impl BuiltinTool {
         ]
     }
 
+    #[allow(dead_code)]
     fn name(&self) -> &'static str {
         match self {
             BuiltinTool::Read => "read",