Step 162: add help panel and documentation

docs/help.md

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+# Documentation
+
+Welcome to Whetstone. This panel provides a compact reference to the editor,
+annotations, agent APIs, and language support.
+
+## Getting Started
+- Open a folder from File > Open or Project > Open.
+- Use the left File Tree to browse files.
+- Toggle Text/Structured mode with the Mode switch in the toolbar.
+- Run or build from the Build tab (or toolbar buttons).
+
+## Annotation Reference
+Whetstone uses canonical memory annotations:
+- `@Reclaim(Tracing|Escape|Cycle)`
+- `@Owner(Single|Shared_ARC)`
+- `@Lifetime(RAII)`
+- `@Deallocate(Explicit)`
+- `@Allocate(Static|Register|Allocator)`
+
+Annotations can be added from the gutter or context menu. Conflicts are
+highlighted in the Problems panel with quick fixes.
+
+## Keyboard Shortcuts
+Shortcuts are configurable. See Settings > Keybindings. Default profile:
+- `Ctrl+P` Command palette
+- `Ctrl+F` Find/Replace
+- `Ctrl+S` Save
+- `Ctrl+Z` Undo, `Ctrl+Y` Redo
+
+## Language Support
+Supported languages (parsing + generation):
+- Python, C++, Elisp, JavaScript, TypeScript, Java, Rust, Go
+
+## Agent API (JSON-RPC)
+Core RPC methods:
+- `getAST`
+- `applyMutation`
+- `generateCode`
+- `getAnnotationSuggestions`
+- `applyAnnotationSuggestion`
+- `startWorkflowRecording`, `stopWorkflowRecording`, `replayWorkflow`
+
+## Troubleshooting
+- If an AST is unavailable, switch to Structured mode.
+- If LSP is offline, completions still work from indexed stubs.
+- If Emacs integration fails, check the Output panel for Emacs logs.