fix: resolve template paths with leading slashes and framework subfolders

[Swahjak]

Summary

Fixes #64

This PR addresses the "Template not found" issue that affected users in several scenarios:

• Leading slash on directory paths: When Symfony's debug:twig returns paths like /templates instead of templates, they were incorrectly treated as absolute filesystem paths, causing the language server to look for templates at the filesystem root instead of the workspace.

• Workspace is parent of Symfony root: When the workspace is a parent folder (e.g., monorepo with app/composer.json), template paths from Symfony were resolved relative to the workspace instead of the PHP project root.

• Bundle namespaces not auto-detected: When working inside bundle directories, templates with @BundleName/... namespace weren't automatically found.

Changes

• Add normalizeTemplatePath.ts utility with:
  • normalizeDirectoryPath(): Handles leading slashes, absolute paths, and composer root resolution
• Add twiggy.composerRoot config setting for projects in subdirectories
• Update DocumentCache to normalize paths and try composer root fallback when resolving templates
• Update CompletionProvider to use normalized template mappings for completions
• Add twiggy.templatePaths config setting for manual namespace registration
• Add tests for path normalization utilities

Why composerRoot instead of inferring from console path?

The previous approach inferred the framework root from symfonyConsolePath (e.g., app/bin/console → app). We replaced this with an explicit composerRoot setting because:

1. Explicitness over inference: Users set composerRoot: "app" directly rather than relying on implicit path parsing
2. Separation of concerns: The console path setting is purely for finding the console, not for determining project structure
3. Better framework support: Works with Craft CMS and vanilla Twig projects that may not use bin/console but still need subdirectory support
4. Simpler code: Removes edge-case handling for extracting paths from console path

Configuration Options

Users can now:

1. Use subdirectory PHP installations (monorepo setups):

{
  "twiggy.composerRoot": "app",
  "twiggy.symfonyConsolePath": "bin/console"
}

The console path is resolved relative to composerRoot, so templates resolve correctly.

2. Configure manual template path mappings:

{
  "twiggy.templatePaths": [
    { "namespace": "@MyBundle", "path": "src/MyBundle/templates" },
    { "namespace": "@Components", "path": "components" }
  ]
}

Test plan

• Build succeeds (pnpm build)
• Path normalization tests pass
• Manual testing with Symfony project having leading slash paths
• Manual testing with monorepo structure (composerRoot: "app")
• Manual testing with bundle development using @BundleName/... namespace