fix: count every file in a new directory, not the directory

[omartelo]

Problem

A session writing a whole new package showed 4 changed files in the footer and on its session card, while the Review tab listed 25.

Diff counted the lines of git status --porcelain. Git's default --untracked-files=normal collapses an untracked directory into one entry:

 M a.txt
?? src/          <- 2 new files in here, reported as 1

The +1175 -0 line totals were right the whole time — they come from ls-files --others --exclude-standard, which lists files, never directories.

Fix

Pass --untracked-files=all to the status call (internal/project/project.go). One flag; the untracked-line counting below it is unchanged.

worktree.go also runs status --porcelain, but only to decide dirty vs clean — the collapse cannot change that answer, so it stays as is.

Test plan

• New case in TestDiff: two untracked files inside a fresh nested directory. Reports Files:4 without the flag (the exact symptom), Files:5 with it.
• gofmt -l . clean, go vet ./... clean, go test ./... — 400 passed.
• Frontend gate green even though it is untouched: biome check clean (12 pre-existing a11y warnings), vitest run 406 passed in 43 files, tsc --noEmit clean, vite build succeeds.