Add Discord channel message puller

uv script that fetches messages from a channel for the last N hours via
the Discord REST API and saves them as JSON for use with jq.

README.md

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+# pull-messages-from-discord
+
+Pull messages from a Discord channel for the last N hours and save them as JSON.
+
+## Setup
+
+Put the bot token in `.env` (gitignored):
+
+```
+HM_DISCORD_BOT_TOKEN=...
+```
+
+The bot needs View Channel + Read Message History on the channel, and the
+Message Content Intent enabled in the Developer Portal (otherwise `content`
+and `embeds` come back empty).
+
+## Usage
+
+```
+uv run script.py --channel homelab-alerts --time 24h
+uv run script.py -c homelab-alerts -t 24
+```
+
+Options: `-c/--channel` (required), `-t/--time` hours, `24` or `24h` (default 24),
+`-g/--guild` name or ID if the channel name is ambiguous, `-o/--output` file path.
+
+Output goes next to the script: `discord_<channel>_<UTC timestamp>.json`.
+
+## jq examples
+
+```
+jq '.count' discord_homelab-alerts_*.json
+jq -r '.messages[] | "\(.timestamp) \(.content)"' file.json
+jq '.messages[].embeds[].title' file.json
+jq '.messages[] | select(.content | test("error"; "i"))' file.json
+```