Add interactive setup wizard for first-run configuration

Introduces `near-agent setup` command that guides users through:
- NEAR AI authentication (reuses existing OAuth flow)
- Model selection (fetches from API or shows defaults)
- Channel configuration (HTTP webhook, Telegram)

Features:
- First-run detection: auto-runs wizard if no session exists
- Respects existing settings: shows current model with keep/change option
- Saves channel secrets to ~/.near-agent/secrets/ with 0600 permissions
- Validates Telegram bot tokens via API before saving

Also fixes default NEARAI_BASE_URL to use cloud-api.near.ai (api.near.ai
returns 410 Gone).

Co-Authored-By: Claude Opus 4.5 <[email protected]>

src/cli/mod.rs

@@ -2,6 +2,7 @@
 //!
 //! Provides subcommands for:
 //! - Running the agent (`run`)
+//! - Interactive setup wizard (`setup`)
 //! - Managing WASM tools (`tool install`, `tool list`, `tool remove`)
 //! - Managing secrets (`secret set`, `secret list`, `secret remove`)
 
@@ -38,6 +39,10 @@ pub struct Cli {
     /// Configuration file path (optional, uses env vars by default)
     #[arg(short, long, global = true)]
     pub config: Option<std::path::PathBuf>,
+
+    /// Skip first-run setup check
+    #[arg(long, global = true)]
+    pub no_setup: bool,
 }
 
 #[derive(Subcommand, Debug)]
@@ -45,6 +50,17 @@ pub enum Command {
     /// Run the agent (default if no subcommand given)
     Run,
 
+    /// Interactive setup wizard
+    Setup {
+        /// Skip authentication (use existing session)
+        #[arg(long)]
+        skip_auth: bool,
+
+        /// Reconfigure channels only
+        #[arg(long)]
+        channels_only: bool,
+    },
+
     /// Manage WASM tools
     #[command(subcommand)]
     Tool(ToolCommand),