JJUI Log (Current File) revset is incorrect in monorepos: path is resolved from project dir, not nearest .jj/ directory

[Straffern]

Summary:
When using JJUI Log (Current File) within a monorepo or workspace, the generated revset/fileset uses Neovim's working directory as the base rather than the nearest .jj/ directory. This causes issues when the project contains multiple projects/repositories or workspace roots, as logs may be run from the wrong context.

Steps to reproduce:

1. Open a file in a subdirectory (e.g. api/) within a monorepo containing multiple .jj/ roots.
2. Run JJUI Log (Current File).
3. Observe that the log revset is built using the project dir instead of the closest .jj/ root.

Expected behavior:

• The revset/fileset should always use the path relative to the closest .jj/ directory (repo root), not Neovim's project dir.
• This behavior should also support workspaces.

Relevant code:

• lua/jjui.lua:jjui_filter_current_file()

  function M.jjui_filter_current_file()
    ...
    local file = vim.fn.expand('%:p')
    if not utils.get_repo_root() then return end
    M.jjui('-r "files(' .. vim.fn.shellescape(vim.fn.fnamemodify(file, ':.')) .. ')"')
  end

• lua/jjui/utils.lua:get_repo_root()
• The path is constructed relative to current working directory, not repo root.

Additional notes:

• JJUICurrentFile does cd to the file's directory, but JJUIFilterCurrentFile does not normalize to repo root.
• Supports monorepo and workspace workflows if adjusted.

Proposed fix:

• Use get_repo_root() to detect the nearest .jj/ directory and make the fileset path relative to it.
• If possible, align revset construction for JJUI Log (Current File) with repo root resolution logic.