docs: remove internal launch state from public documentation

[brendanjryan]

Goal

Make repository documentation appropriate for a permanently public project. Keep transient launch status and private repository topology in issue #2 rather than committed documentation.

Scope

• Remove “The repository stays private until launch approval” from submissions/README.md.
• Replace the “Private validation” and “Public launch step” tracker columns with durable platform requirements, or move the tracker entirely into issue Track marketplace submissions #2.
• Remove transient status such as “deploy MCP fixes,” “complete policy gap,” and “submit draft.”
• Remove private-install and public-launch-approval wording from submissions/claude.md and submissions/mcp-registries.md.
• Rework README.md so it explains that Mercator content is synchronized without describing the source repository as private.
• Rework CONTRIBUTING.md to avoid publishing private repository paths, token implementation details, and mutable branch-policy state.
• Review the remaining submissions/ documents for roadmap or review-state language and move any transient tracking into issue Track marketplace submissions #2.

Preserve

• Public installation and submission instructions.
• User-facing security language, including private vulnerability reporting and warnings against sharing private keys.
• Necessary contributor guidance that generated Mercator files must not be edited directly.
• Accurate disclosure of plugin capabilities and marketplace eligibility.