Replace mdsh with esh for template processing

- Vendor esh script (MIT licensed) into lib/esh/
- Remove mdsh dependency from Cargo.toml
- Update prompts.rs to use esh instead of mdsh
- Extract load_system_md helper for cleaner code
- Simplify system prompt change logging
- Update README with esh syntax examples

Syntax: <%= $(command) %> for substitution, <% code -%> for control flow

Author: tcdent

Cargo.lock

@@ -51,9 +51,6 @@ clap = { version = "4", features = ["derive", "env"], optional = true }
 anyhow = "1"
 thiserror = "2"
 
-# Markdown shell preprocessor (for dynamic system prompts)
-mdsh = { git = "https://github.com/zimbatm/mdsh" }
-
 # Utilities
 fancy-regex = "0.14"
 unicode-width = "0.2"

Cargo.toml

@@ -94,20 +94,21 @@ You can extend Codey's system prompt by creating `SYSTEM.md` files that are auto
 1. **User config**: `~/.config/codey/SYSTEM.md` - personal customizations
 2. **Project**: `.codey/SYSTEM.md` - project-specific instructions
 
-### Dynamic Content with mdsh
+### Dynamic Content with esh
 
-SYSTEM.md files support [mdsh](https://github.com/zimbatm/mdsh) syntax, allowing you to embed shell commands that are executed dynamically. This is useful for including context that changes over time.
+SYSTEM.md files support [esh](https://github.com/jirutka/esh) (Embedded SHell) syntax, allowing you to embed shell commands that are executed dynamically. This is useful for including context that changes over time.
 
 ### Example SYSTEM.md
 
 ```markdown
-Today is `$ date '+%d %B %Y'`.
+## Environment
 
-```$
-if which linctl > /dev/null 2>&1; then
-  echo "Use linctl to manage Linear tickets."
-fi
-```
+- Today's date: <%= $(date +"%m-%d-%Y") %>
+- Project root: <%= $(pwd) %>
+
+<% if which linctl > /dev/null 2>&1; then -%>
+Use linctl to manage Linear tickets.
+<% fi -%>
 
 ## Guidelines
 - Follow the existing code style

README.md

@@ -0,0 +1,21 @@
+The MIT License
+
+Copyright 2017-present Jakub Jirutka <jakub@jirutka.cz>.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.