feat: add file content identification with MIME type detection

[Copilot]

Adds automatic content type detection to identify HTTP requests, URL lists, and file MIME types.

Changes

New pkg/contentid package

• MIME type detection via gabriel-vasile/mimetype
• HTTP request detection (GET/POST/etc with headers)
• URL list detection (70%+ URL content threshold)
• Pure Go implementation, no CGO dependencies

CLI integration

• Added -identify flag for standalone content identification
• Supports both human-readable and JSON output (-jsonl)
• Works with existing -f and -l file input flags

Usage

# Human-readable output
ph -identify -f /path/to/files/*.txt

# JSON output
ph -identify -jsonl -f /path/to/files/*.txt

Example output:

/tmp/request.txt: HTTP request [text/plain; charset=utf-8] (HTTP Request)
/tmp/urls.txt: URL list [text/plain; charset=utf-8] (URL List)
/tmp/data.json: JSON data [application/json]

Note: Uses mimetype library instead of magika to avoid CGO/ONNX Runtime complexity while providing equivalent functionality for the use case.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com//advisories
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>feat: add file content identification</issue_title>
<issue_description>ph should be able to detect what type of content it is (raw request, file with urls, etc...)

We can use magika for this.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes feat: add file content identification #1

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