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.

skills/custom-skill-prompt/README.md

@@ -0,0 +1,21 @@
+# meeting-agenda
+
+Generate a structured meeting agenda from a topic and duration. Pure prompt engineering — no code required.
+
+## Configuration
+
+| Field | Value |
+|-------|-------|
+| Type | `promptonly` |
+| Entry | N/A (template-only) |
+
+## Input
+
+- **topic** (string, required) — The meeting topic
+- **duration_minutes** (string, required) — Meeting duration in minutes
+
+## Usage
+
+```bash
+librefang skill test ./skills/custom-skill-prompt --input '{"topic": "Q1 planning", "duration_minutes": "30"}'
+```