Modernize .vscode/tasks.json to the 2.0.0 schema

[dawsbot]

Problem

.vscode/tasks.json still uses the deprecated "version": "0.1.0" task schema (isShellCommand, showOutput, top-level command/args). Every time the extension is launched with F5, VS Code auto-migrates the file and drops a .vscode/tasks.json.old backup, producing spurious local diffs and editor cruft on every run.

VS Code's own auto-migration is also malformed: it leaves the old top-level command/args keys and appends a nested tasks array.

Fix

Replace it with a clean, hand-written 2.0.0 tasks file so VS Code stops re-migrating it. Rough target:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "compile",
            "type": "npm",
            "script": "compile",
            "isBackground": true,
            "problemMatcher": "$tsc-watch",
            "group": "build"
        }
    ]
}

• Confirm F5 / "Run Extension" still triggers the watch build via the compile script.
• Consider gitignoring *.old (or .vscode/*.old) as a belt-and-suspenders guard against the backup files.

Context

Split out of #73. Deferred to a dedicated upcoming PR to keep #73 focused on the no-match fuzzy suggestions.