Secure hosted MCP credential setup

[hmishra2250]

Summary

Updates firecrawl setup mcp so hosted MCP credentials are sent as authorization headers instead of being embedded in the server URL.

• Always configures the hosted endpoint as https://mcp.firecrawl.dev/v2/mcp.
• Adds Authorization: Bearer ... only when an API key is available.
• Keeps setup keyless when no API key is configured.
• Uses client-native environment references for Cursor, OpenCode, and global Codex setup when FIRECRAWL_API_KEY supplies the active key.
• Pins add-mcp@1.14.0 so generated client configuration remains reproducible.
• Replaces secret-bearing shell command strings with argument-based process execution.
• Stops printing installer commands or OpenClaw child output that may contain credentials.
• Preserves existing Hermes YAML and restricts its credential-bearing configuration file to mode 0600 on POSIX systems.

Compatibility

• Existing agent aliases, global/local selection, all-launcher setup, confirmation flags, and quiet output remain supported.
• Claude Code, VS Code, Codex, OpenCode, Cursor, Hermes, and OpenClaw continue to receive their existing setup shape with the corrected endpoint and authentication placement.
• This change does not configure the browser OAuth endpoint; the CLI continues to use keyless or API-key access on /v2/mcp.

Verification

• Targeted setup tests: 28 passed.
• Full test suite: 23 files, 372 tests passed.
• TypeScript, build, formatting, and diff checks pass.
• Credential scans find no API key in hosted MCP URLs or wrapper output.
• Adversarial credentials containing command substitutions, backticks, quotes, newlines, and environment references remain inert.
• Isolated add-mcp@1.14.0 smokes confirm Cursor and OpenCode environment references and literal header configuration for other supported clients.
• A real Codex smoke writes bearer_token_env_var = "FIRECRAWL_API_KEY" without persisting the key.
• Keyless Hermes and OpenClaw smokes contain no authentication fields.

Shared hosted MCP contract

• Version: 1.0.0
• SHA-256: ef000059d2e9b57d88db34441bffb0f3249ae0ac3b5d85d5ce60dd2343366c2c
• Authoritative artifact: firecrawl-mcp-server/contracts/hosted-mcp/v1/contract.json
• This PR covers: Header-based unattended setup.

Review and deploy this PR against the same contract version and hash.