Simplify system prompt: remove coding style and parallel tool call sections

- Remove IMPORTANT FOR CODING section (~1,500 chars of coding guidelines)
- Remove <use_parallel_tool_calls> block (~500 chars)
- Remove unused const_format dependency from g3-core
- Simplify get_system_prompt_for_native() to just return base prompt
- Response Guidelines now cleanly ends the static prompt

Prompt reduced from ~8,500 to ~6,500 characters.

crates/g3-core/src/tools/mod.rs

@@ -8,9 +8,11 @@
 //! - `webdriver` - Browser automation via WebDriver
 //! - `misc` - Other tools (screenshots, code search, etc.)
 //! - `research` - Web research via scout agent
+//! - `memory` - Project memory (read_memory, remember)
 
 pub mod executor;
 pub mod file_ops;
+pub mod memory;
 pub mod misc;
 pub mod research;
 pub mod shell;