docs(snapshot/README): Add Capabilities and Limitations table

why: Clarify module boundaries and set appropriate user expectations

what: - Added a clear tabular format separating what the module can and cannot do - Highlighted key capabilities with checkmarks - Identified important limitations with X marks

Author: tony

src/libtmux/snapshot/README.md

@@ -23,6 +23,19 @@ Snapshots provide several key benefits for tmux automation and management:
 - **Filtering & Searching:** Find specific components within complex tmux arrangements
 - **Dictionary Conversion:** Serialize tmux state for storage or analysis
 
+## Capabilities and Limitations
+
+| What It IS | What It IS NOT |
+|------------|----------------|
+| ✅ **Structure Preserver**: Captures hierarchical tmux objects (servers, sessions, windows, panes) | ❌ **Memory Snapshot**: Doesn't capture system memory state or processes beyond tmux |
+| ✅ **Immutable Reference**: Creates read-only records that won't change as live tmux changes | ❌ **Time Machine**: Can't revert the actual tmux server to previous states |
+| ✅ **Content Capturer**: Preserves visible pane text content when requested | ❌ **State Restorer**: Doesn't automatically recreate previous environments |
+| ✅ **Relationship Keeper**: Maintains parent-child relationships between tmux objects | ❌ **App State Preserver**: Can't capture internal application state (e.g., vim buffers/cursor) |
+| ✅ **Filtering Tool**: Provides ways to search objects based on custom criteria | ❌ **Server Modifier**: Doesn't change the live tmux server in any way |
+| ✅ **Serialization Mechanism**: Converts tmux state to dictionaries for storage | ❌ **Process Manager**: Doesn't track processes beyond their visible output |
+| ✅ **Testing Aid**: Enables tmux automation tests with before/after comparisons | ❌ **Complete Backup**: Doesn't capture scrollback buffers or hidden app state |
+| ✅ **Configuration Recorder**: Documents session layouts for reference | ❌ **System Restorer**: Can't restore the full system to a previous point in time |
+
 ## Installation
 
 The snapshot module is included with libtmux: