Fix misleading debug startup errors

[Oz Zafar (ozzafar)]

Summary

Fixes #144.

• Report the matching pre-launch task name, nonzero exit code, and launch configuration instead of incorrectly suggesting that a language extension is missing.
• Track newly started task executions within the relevant workspace, including labeled dependencies, and report failures even while VS Code is waiting on its task-error dialog.
• Preserve startup and Testing API errors. Cancel readiness waits and dispose their listeners when startup finishes or fails.
• Add regression coverage and update the changelog and architecture documentation.

Validation

• npm test -- --code-version 1.134.0 --timeout 15000: 179 passing, including compile, bundle, and lint via pretest. Obsolete generated test output with no corresponding source on this branch was archived before the clean run.
• Reproduced the reporter's PowerShell Copy-Item positional-parameter error in a normal, isolated VS Code 1.134.0 window using a real launch.json, tasks.json, and MCP HTTP request through the production routing/control path.
• MCP returned an error identifying the failed task and exit code 1 in approximately 1.5 seconds while the real task-error dialog remained open.
• Confirmed Abort leaves no debug session and Debug Anyway starts the real Node debugger and pauses at the fixture breakpoint. Stopped the debugger, cleared fixture breakpoints, and closed the isolated window afterward.

Limitations

VS Code task events do not expose terminal output and may omit an exit code. Responses point to the task terminal for the original command error and use neutral guidance when no specific failure is available. Reporting a task failure does not dismiss VS Code's dialog or cancel its pending launch request. Task-identifier objects and dynamically supplied task configurations are left to VS Code rather than resolved by the diagnostics observer.

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