docs: update docs (#43)

- macOS, Linux badge and AI suggestions showcase in README
- Update user guide and docs for development

docs/dev/history.md

@@ -0,0 +1,22 @@
+# Shell history integration (`integration/history.go`)
+
+The `history` module provides `Ctrl+R` search functionality by reading the user's persistent shell command history.
+
+## Features
+
+- **Zsh extended support**: Parses `: <timestamp>;<command>` format common in Zsh.
+- **Lazy loading**: Reads disk only when history search is invoked, preserving instant startup performance.
+- **Fuzzy search**: Integrates with the `fuzzy` search engine for match scoring.
+- **Deduplication**: Filters duplicate commands, displaying unique entries.
+
+## Data flow
+
+1. User presses `Ctrl+R`.
+2. `root` sets `mode = "history"`.
+3. `SearchHistory("")` is called.
+4. If cache is empty:
+   - Reads history file (`~/.zsh_history` or `~/.bash_history`).
+   - Strips metadata using delimiters.
+   - Populates command memory cache.
+5. Matches are scored and sorted by the search engine.
+6. Suggestions are returned to `overlay` for rendering.