docs: expand README with detailed script documentation

- Add installation section with copy commands
- Document each script with features, requirements, config examples
- Add practical configuration examples for common use cases
- Update CLAUDE.md with shared library documentation

CLAUDE.md

@@ -13,7 +13,7 @@ just check       # fmt-check + lint (pre-commit gate)
 
 ## Architecture
 
-This repository holds standalone Lua scripts for mpv (0.36+, bundled Lua 5.2). Each script in `scripts/` is self-contained with no external Lua dependencies.
+This repository holds Lua scripts for mpv (0.36+, bundled Lua 5.2).
 
 Script structure convention:
 1. Header comment block explaining features, requirements, and configuration
@@ -21,6 +21,17 @@ Script structure convention:
 3. Note indicating no edits are needed below the config block
 4. Implementation code
 
+### Shared Library
+
+`scripts/lib/utils.lua` contains common utilities (trim, clamp, ASS color helpers). Scripts load it via:
+
+```lua
+package.path = mp.command_native({ "expand-path", "~~/scripts/lib/?.lua;" }) .. package.path
+local lib = require("utils")
+```
+
+When adding new shared functions, prefer adding to this module over duplicating code.
+
 ## Code Style
 
 - 2-space indentation, 100-column width, double quotes preferred (enforced by stylua)