fix: activate contributed commands explicitly

[RasputinKaiser]

What this PR does

Adds explicit VS Code activation events for each contributed Storm Search command.

Why

Closes #39. The reported warning says command 'custom-search.searchInFolder' not found after pressing the contributed keybinding on a fresh install. The command is contributed in package.json and registered in src/extension.ts, but the extension manifest currently has an empty activationEvents array. Explicit onCommand activation events make VS Code activate the extension before running the contributed commands.

Changes

• Adds onCommand:custom-search.openSearch.
• Adds onCommand:custom-search.openNewSearchTab.
• Adds onCommand:custom-search.searchInFolder.

Duplicate check

• Checked issue Command not found #39 comments before implementation; the only comment was the maintainer asking for the VS Code version.
• gh pr list --repo zigcBenx/storm-search --state all --search "39 Command not found" returned no PRs.
• gh pr list --repo zigcBenx/storm-search --state all --search "command not found activationEvents searchInFolder" returned no PRs.

Testing

npm ci
npm run compile
git diff --check

npm run lint is currently blocked by the repository not having an ESLint configuration file, so ESLint exits before linting source files. I did not add unrelated lint configuration in this PR.