docs: add README for every subdirectory

33 agent READMEs, 14 hand READMEs, 2 plugin READMEs
(echo-memory + hooks), and 2 skill READMEs
(custom-skill-prompt + custom-skill-python).

Each README documents the component's purpose, configuration,
and usage based on its TOML definition.

agents/travel-planner/README.md

@@ -0,0 +1,23 @@
+# Travel Planner
+
+Trip planning agent for itinerary creation, booking research, budget estimation, and travel logistics.
+
+## Configuration
+
+| Field | Value |
+|-------|-------|
+| Module | `builtin:chat` |
+| Model | `default` |
+| Provider | `default` |
+
+System prompt instructs day-by-day itinerary creation, destination research, budget planning at multiple tiers, accommodation recommendations, and multi-destination trip optimization.
+
+## Skills
+
+- `file_read`, `file_write`, `file_list`, `memory_store`, `memory_recall`, `web_search`, `web_fetch`, `browser_navigate`, `browser_click`, `browser_type`, `browser_read_page`, `browser_screenshot`, `browser_close`
+
+## Usage
+
+```bash
+librefang agent run travel-planner
+```