feat: consume configure-only CDB workflow

[wellwei]

Summary

• replace the obsolete mcpp ide configure --format ndjson client with mcpp build --configure-only
• validate success through the process exit code and a parseable member/package compile_commands.json, retaining the last known good CDB on failure
• align virtual/rooted workspace discovery, operation locking, manifest routing, trust handling, and CDB watcher behavior with mcpp PR #387
• release the extension as 0.3.0 for automatic CDB generation without compiling normal objects or linking

Closes #5

Upstream contract

• feat: generate compile database without building mcpp#387 is merged as 3f237ed
• the client does not parse human stdout or depend on the broader JSON/NDJSON machine-output RFC

Test plan

• npm test (264 passed)
• npm run test:e2e (1 passed)
• real mcpp build --configure-only consumer check with source and test translation units
• npm run package
• unzip -t mcpp-vscode-0.3.0.vsix
• embedded VSIX manifest reports mcpp-community.mcpp-vscode@0.3.0
• git diff --check