Add gittr, gitnostr, and gittr-mcp

[arbadacarbaYK]

Summary

Adds the gittr stack — git on Nostr (NIP-34) — in the three sections that match how this list is already split:

• Repository Hosting: gittr — public forge UI (repos, issues/PRs, Lightning bounties). Identity is a Nostr key. Source: https://github.com/arbadacarbaYK/gittr
• Self-Hosted Repository: gitnostr — the git server/bridge (SSH + HTTPS bare repos, relay-watched NIP-34 events). Same role as Gitea/Soft Serve, not the website.
• Tools: gittr-mcp — MCP server so AI agents can use gittr with a Nostr identity (stdio; Cursor, Claude, VS Code, …)

They are three repos on purpose: website, git host, agent tools. Live git remote is git.gittr.space.

Test plan

• Links resolve (gittr.space, GitHub gitnostr, GitHub gittr-mcp)
• One line per project, same * [Name](url) - description format
• Not already listed