feat: add complete Fiddle file tree

[icecreamx10]

Summary

• render Fiddle editor files as an expandable directory tree using the existing Blueprint-style visual language
• recursively collect the complete editable showcase source tree, including src/main/desktop and src/main/web
• keep generated output, dependencies, binary files, lockfiles, and oversized text files out of the editor
• rebuild and expand the tree when switching Gallery showcases
• keep documentation and text assets available in the tree without displacing the default code panes

Root cause

The showcase loader stopped after two directory levels and capped snapshots at 14 files. The sidebar then rendered the remaining file IDs as a flat list, so deeper sources such as src/main/desktop/* disappeared entirely.

Validation

• pnpm --dir lynxtron-go exec vitest run src/app/fiddle/runner/workspace-files.test.ts src/app/fiddle/Sidebar/file-tree.test.ts — 4 tests passed
• pnpm --dir lynxtron-go typecheck — passed
• pnpm --dir lynxtron-go build — passed with existing Lynx CSS and dynamic require warnings
• runtime validation with file-explorer and cross-platform-notes: directory expansion/collapse, src/main visibility, and Gallery case switching verified

[changeset-bot]

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Latest commit: 5839e4a

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