Add initial scripts and project conventions

examples/hello-world.md

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+# hello-world.sh
+
+Reference example script — prints a greeting. Demonstrates the required
+structure every script in this repo must follow: `common.sh` sourcing,
+`SCRIPT_HELP` heredoc, `--help` handling, and argument parsing with
+`common::die` on invalid input.
+
+**This is not a real utility.** Copy its structure when writing an actual
+script; don't invoke it from other scripts or automation.
+
+## What it does
+
+Prints `Hello, <name>!` to stdout, where `<name>` defaults to `world` or
+whatever is passed via `--name`.
+
+## Requirements
+
+- Bash 4+ (uses `set -euo pipefail`, no external commands beyond common.sh)
+
+## Usage
+
+```bash
+./examples/hello-world.sh [OPTIONS]
+```
+
+### Options
+
+| Option | Description |
+|--------|-------------|
+| `-h`, `--help` | Show help message and exit |
+| `-n`, `--name NAME` | Name to greet (default: `world`) |
+
+## Examples
+
+```bash
+# Default greeting
+./examples/hello-world.sh
+# → Hello, world!
+```
+
+```bash
+# Custom name
+./examples/hello-world.sh --name Danail
+# → Hello, Danail!
+```