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-core/src/config.rs

@@ -649,6 +649,7 @@ impl ConfigLoader {
     /// - Provider-specific: `GYANDOOT_OPENAI_API_KEY`, `GYANDOOT_OPENAI_MODEL`,
     ///   `GYANDOOT_OPENAI_BASE_URL`, `GYANDOOT_ANTHROPIC_API_KEY`, etc.
     pub fn from_env(&self, config: &mut GyandootConfig) {
+        #[allow(unused_macros)]
         macro_rules! env_opt {
             ($key:literal, $target:expr) => {
                 if let Ok(val) = std::env::var(concat!(env_prefix_str!(), $key)) {
@@ -785,7 +786,7 @@ impl ConfigLoader {
 
 /// Convenience: load config from a single TOML file (legacy API).
 pub fn load_config_from_file(path: &std::path::Path) -> anyhow::Result<AgentConfig> {
-    let loader = ConfigLoader::new();
+    let _loader = ConfigLoader::new();
     let gyandoot = ConfigLoader::from_file(path)?;
     Ok(AgentConfig::from(gyandoot))
 }