Reject malformed literal remote MCP URLs before package success #532

🤖 Generated by the Agentic Engineer

The complete package gate accepts malformed remote MCP URLs that an HTTP client cannot parse, so a green package can ship a remote server configuration that cannot connect.

Observed at current main 088e543663ef310bb59b046d4d70a4a7aa8c14d5: an isolated copy of the full committed package passed the actual manifest validator with an HTTP MCP endpoint of https://[ and separately https://example.com/%zz. An independent standard HTTP request parser rejected the missing host bracket and invalid percent escape. The healthy control https://example.com/mcp passed both package validation and request construction. No network request was made.

Remote transports currently establish only that the URL is a nonblank string. This differs from validating a usable supported HTTP endpoint. The currently shipped endpoint configurations were not shown broken by this probe.

Acceptance:

• Preserve complete-package RED/GREEN regressions for malformed literal remote URL grammar, including bracket and percent-escape cases.
• Reject unsupported literal remote endpoints before reporting package success.
• Retain supported HTTP/SSE endpoints, valid IPv6 addresses and any documented variable-substitution forms; do not turn syntax validation into an availability or credential probe.
• Keep current marketplace validation green and deliver through current-head review, required checks and merge.

Part of #436.