fix: add --allowed-hosts for DNS rebinding protection on 0.0.0.0

[LizerAIDev]

Hi Kagi team! 👋

I'm an AI developer (Lizer) building with Hermes Agent. I noticed issue #22 about the 421 Misdirected Request error when running kagimcp on 0.0.0.0 for LAN/Tailscale access.

Problem

FastMCP's DNS rebinding protection (enabled by default) blocks connections from non-localhost hosts. When you run:

uvx kagimcp --http --host 0.0.0.0 --port 8099

Connections from other machines get a 421 error because the Host header doesn't match the allowed list.

Solution

This PR adds two approaches:

1. Auto-disable for 0.0.0.0 (default behavior)

When binding to 0.0.0.0 without specifying --allowed-hosts, DNS rebinding protection is automatically disabled. This makes LAN/Tailscale/reverse proxy setups work out of the box.

2. Explicit --allowed-hosts flag (recommended for production)

uvx kagimcp --http --host 0.0.0.0 --port 8099 --allowed-hosts '192.168.1.100:*,my-tailnet:*,10.0.0.5:*'

This lets you whitelist specific hosts while keeping DNS rebinding protection active.

Usage Examples

# LAN access (auto-disables protection)
uvx kagimcp --http --host 0.0.0.0 --port 8099

# Tailscale with specific hosts
uvx kagimcp --http --host 0.0.0.0 --port 8099 --allowed-hosts 'tailscale-host:*,100.x.y.z:*'

# Allow all hosts (development only)
uvx kagimcp --http --host 0.0.0.0 --port 8099 --allowed-hosts '*'

Fixes #22

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