* feat(file-token): add file: inline metadata token with gf navigation
Problem: there was no way to link a task to a specific location in a
source file, or to quickly jump from a task to the relevant code.
Solution: add a file:<path>:<line> inline token that stores a relative
file reference in task._extra.file. Virtual text renders basename:line
in a new PendingFile highlight group. A buffer-local gf mapping
(configurable via keymaps.goto_file) opens the file at the given line.
M.add_here() lets users attach the current cursor position to any task
via vim.ui.select(). M.edit() gains -file support to clear the
reference. <Plug>(pending-goto-file) and <Plug>(pending-add-here) are
exposed for custom mappings.
* test(file-token): add parse, diff, views, edit, and navigation tests
Problem: the file: token implementation had no test coverage.
Solution: add spec/file_spec.lua covering parse.body extraction,
malformed token handling, duplicate token stop-parsing, diff
reconciliation (store/update/clear/round-trip), LineMeta population
in both views, :Pending edit -file, and goto_file notify paths for
no-file and unreadable-file cases. All 292 tests pass.
* style: apply stylua formatting
* fix(types): remove empty elseif block, fix file? annotation nullability