feat(examples): add Antigravity Chat UI (leptos_ssr_axum) and agent_server SSE proxy

agent_server/src/main.rs
- Full Axum HTTP server that proxies the Antigravity SDK over SSE
- Endpoints: POST /chat/stream (SSE), POST /confirm, POST /halt,
  POST /answer, GET|POST /workspace, GET /sessions, POST /sessions/rename
- ConfirmHook: per-session tool-approval gate; supports once / allow-for-session
- Auto-approves read-only tools (VIEW_FILE, LIST_DIRECTORY) immediately
- Concurrent confirm-task runs alongside step-stream loop so confirmations
  never block token delivery
- SSE keepalive (15 s ping) + 2 048-slot channel buffer prevent connection
  drops during long-running agent turns
- Per-session workspace isolation; WORKSPACE_ROOT env override supported

agent_server/Cargo.toml
- Added axum, tokio, serde, tracing, anyhow, gloo dependencies

agent_server/rust_async_learning/
- Generated Rust async learning workspace produced by the agent during a
  live teaching session (compiler-driven development demo)

leptos_ssr_axum/src/app.rs
- Full chat UI built on Leptos 0.7 + WASM hydration
- SSE EventSource client: token / thought / tool_start / tool_result /
  confirm / usage / idle / done / error named events
- Floating permission panel above input for tool confirmations;
  Deny now also calls POST /halt to stop the agent immediately
- AssistantMessage blocks rendered with markdown + syntax highlighting
- Thinking blocks (collapsible THOUGHT PROCESS chip)
- ToolCall / ToolResult cards with status badges and output accordion
- Usage summary badges per agent turn
- Sidebar session list with rename (persisted to KV, merge strategy
  prevents server list refresh from clobbering local renames)
- Dark/light theme toggle persisted to localStorage
- Auto-scroll with user-scroll-up detection
- Session-scoped stream_completed flag prevents double-finalisation

leptos_ssr_axum/src/server.rs
- Spin KV backed session persistence: save_turn_blocks, list_sessions,
  rename_session, get_session_blocks server functions

leptos_ssr_axum/src/types.rs
- MessageBlock, SessionMeta, PendingConfirm, SSE event structs

leptos_ssr_axum/src/main.rs + Cargo.toml + input.css
- Spin/WASM entry point, dependency manifest, Tailwind input stylesheet

leptos_axum/src/lib.rs
- Minor fixes to the simpler leptos_axum example

Author: codeitlikemiley

examples/agent_server/Cargo.toml

@@ -19,3 +19,4 @@ tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 dotenvy = "0.15"
 futures-util = "0.3"
+anyhow = "1"

examples/agent_server/rust_async_learning/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "rust_async_learning"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

examples/agent_server/rust_async_learning/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}