Introduce the ability to reveal specific sections of a document
rather than entire files. This includes:
- Updating `revealedPaths` to map normalized file paths to sets of
revealed section slugs.
- Adding `isPathRevealed` to handle visibility logic for connected
clients and GMs.
- Enhancing `extractHeadings` to calculate `startLine` and `endLine`
for each TOC node to support precise section identification.
Introduce a dialog for switching between built-in content and a
user-selected local folder. Persist the folder handle in IndexedDB
so the selection survives page refreshes. Scan the folder for .md,
.yarn, and .csv files to build the file index.
Update App and Sidebar to pass file tree and heading data, and
add TypeScript declarations for the File System Access API.
hypercross
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