Desktop: line-anchored comments and file browsing exist, but only inside PRs — can they reach ordinary project files?

## The ask, in one line

Desktop can show a repo's files and let you comment on a specific line — but only inside a pull request. Can that same pair of capabilities reach a project's **ordinary files**, outside of a proposed change?

## Why this is a join, not a new feature

Both halves already exist in this repo:

- **Line-anchored comments** — `desktop/src/features/projects/ui/ProjectPullRequestInlineComments.tsx` renders a thread anchored to `{path, line}` with a *"Leave a comment on this line…"* composer. Diff rows and hunk parsing live in `ProjectPullRequestFilesChangedPanel.tsx`.
- **Repo file browsing** — `web/src/features/repos/ui/` has `RepoTreeSection`, `RepoBlobViewer`, `RepoRefsSection`, `RepoCommitsSection`, `RepoReadmeSection`. A complete browser, with sensible content-type and preview-size safety in the blob viewer.

What does not exist is the combination: open an arbitrary file at HEAD in Desktop and anchor a comment to a line in it.

## The workflow this unlocks

Agent-assisted development where a human reviews code and leaves a targeted instruction *before* any change is proposed:

1. Open the project, browse to a file
2. Comment on the specific line — "this needs to handle the empty case"
3. An agent in the channel picks that up and opens a PR

Today step 1-2 require an existing PR, so the human can only react to a change an agent already made. The pre-change direction is the missing half, and it is the more valuable one.

## Questions

1. Is file browsing intentionally web-only, or simply not yet ported to Desktop?
2. Would you accept line-anchored comments on non-PR file paths, or is the anchor deliberately scoped to a diff? Comments are kind:1 with an anchor — a file-at-ref anchor seems expressible in the same shape, but I do not want to assume your model.
3. If this is wanted, is the preferred direction porting the web tree/blob components to Desktop, or something else?

Happy to send the PR if there is a direction and it is wanted. Asking first because this touches core surfaces rather than a corner, and I would rather build the shape you want than guess.

## Related

- #3728 — NIP-34 issues lack hierarchy/dependency/frontier (agent work pipelines)
- #3611 — project↔channel tag mismatch (`h` / `project-channel` / `buzz-channel`), no writer