feat(auth): forward SONARQUBE_TOKEN to upstream as Bearer header

The upstream MCP container requires a SonarQube user token in the
Authorization header. Without one, every call returns 401.

- proxy: read SONARQUBE_TOKEN via sonarqube_token() at session-open
  time; raise TokenMissingError when unset/blank. upstream_session()
  attaches the token as "Authorization: Bearer <token>" via
  streamablehttp_client(headers=...).
- cli: fail fast in serve and check with a clear stderr message and
  exit 1 when the token is missing, before any network attempt. All
  exception text written to stderr passes through _redact() so an
  accidentally-leaked token from a third-party exception is replaced
  with [REDACTED] before display.
- The token is never stored on any object, never logged, and the
  TokenMissingError message contains no token material (it only
  describes how to generate one in SonarQube).
- Tests: header forwarding via mocked streamablehttp_client, missing-
  token exit code, redaction in CLI error paths, whitespace stripping
  on the token. Total: 25 tests.
- Docs: README/CLAUDE updated with the new env-var, Claude Desktop
  config snippet, and the security guarantees. CHANGELOG added.

Bumps version to 0.2.0.

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

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "mcp-sonarqube-proxy"
-version = "0.1.0"
+version = "0.2.0"
 description = "Stdio MCP server that proxies tools from an upstream SonarQube MCP server over streamable HTTP."
 readme = "README.md"
 requires-python = ">=3.12"