docs(mcp): rewrite README for end users (#345)

The published README was 1346 lines and full of internal planning language
(Phase 6/7/8/9, decision IDs like D7-03, "killer-app" framing, raw Prisma
model names) plus a 1000+ line per-tool schema dump — confusing for anyone
who just wants to use the package.

Replace it with a concise (~185 line) end-user guide: quick start,
configuration, token scopes, Claude Desktop / Cursor setup, a compact tool
reference table (the MCP client discovers full parameter schemas at runtime),
diagnostics, and security. Adds a patch changeset so the new README reaches
the npm page on the next release.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: therealbrad

.changeset/mcp-readme-rewrite.md

@@ -0,0 +1,5 @@
+---
+"@testplanit/mcp-server": patch
+---
+
+Rewrite the README as concise, plain-English usage documentation: quick start, configuration, client setup, and a compact tool reference. Removes internal planning jargon and the 1000+ line per-tool schema dump (the MCP client discovers parameters at runtime).