404 handling and branch names with / in remote space URLs #65

Bug

Visiting a remote space URL with a branch containing / fails with an unhelpful error.

Current Behavior

Visiting:

https://nsheaps.github.io/cept/pr-52/g/github.com/nsheaps/cept/blob/claude/setup-and-fix-issues-YhySm/docs/git-content-getting-started-quick-start-md

Shows error: "could not find claude"

Problems

1. No proper 404 page

When a path segment can't be resolved, the app should show a proper 404 page with:

• Clear information about what went wrong (which part of the path couldn't be found)
• Enough functionality for the user to recover (navigation still works, sidebar functions, links to go elsewhere)
• If not in a space context, the sidebar should behave accordingly (not break)

2. Branch names with / not handled

Branch names like claude/setup-and-fix-issues-YhySm contain / which the URL parser is splitting incorrectly — it finds claude as a path segment and fails instead of recognizing the full branch name.

The URL routing needs to handle branches with / in them, likely by:

• Trying progressively longer path segments as branch names
• Using the GitHub API to validate branch existence
• Or encoding the branch name differently in the URL

Context

From PR #52 follow-up issues.