Add configurable HTTP host support and worker provider presets

[hotwa]

Summary

This PR adds two small but useful capabilities for running maniple as a persistent MCP service and for integrating Claude-compatible provider wrappers without hard-coding local secrets into
the repository.

1. Configurable HTTP host and host allowlist

maniple can now run streamable HTTP on a configurable bind address instead of always using 127.0.0.1.

Added CLI options:

• --host
• --allow-host
• --allow-origin
• --disable-dns-rebinding-protection

This makes it possible to run the MCP server on a LAN/Tailscale address while still keeping FastMCP host/origin protection configurable.

2. Worker provider presets and per-worker command/env overrides

Workers can now be launched with either:

• a named provider preset from ~/.maniple/config.json, or
• direct command / env overrides

This keeps the core orchestration logic generic while allowing users to plug in local Claude-compatible wrappers.

The repo also adds a small example wrapper script:

• scripts/claude-maniple-switch

The documented pattern is:

• main config: ~/.maniple/config.json
• provider credentials: ~/.maniple/.env
• wrapper executable: ~/bin/claude-maniple-switch

This avoids baking user-specific .env paths, credentials, or provider naming conventions into the repository.

Why

I wanted a minimal approach that:

• works well for persistent HTTP deployment
• supports multiple Claude-compatible providers
• keeps secrets out of the repo
• does not tightly couple maniple to any one local provider management setup
• remains easy to rebase onto upstream changes

Implementation Notes

• HTTP transport creation now accepts explicit transport security settings.
• spawn_workers resolves named provider presets from config.
• provider cannot be mixed with direct command / env overrides on the same worker.
• Claude wrapper commands can still receive --settings when appropriate so stop-hook based idle detection continues to work.
• The example wrapper loads provider-specific credentials from ~/.maniple/.env after sourcing the local provider switch script, so maniple-specific credentials can override shell defaults
  cleanly.

Tests

Added/updated tests for:

• HTTP CLI host/security flags
• config parsing and persistence for provider presets
• CLI backend command override behavior
• spawn_workers provider resolution and validation
• wrapper dispatch and .maniple/.env loading

Test command used:

uv run pytest tests/test_config.py tests/test_cli_backends.py tests/test_spawn_workers_defaults.py tests/test_claude_maniple_switch.py tests/test_server_http_cli.py tests/
test_server_terminal_backend_fallback.py

## PR Checklist

- [x] Backend parity: tmux + iterm
- [x] Tests cover both backends where applicable
- [x] uv run pytest passes for the targeted changed areas