docs: Add specs and tasks for previously scoped work in todo.md

.config/dot/.claude/tasks/0008-folders-collision-handling.md

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+---
+spec: dot-setup-folders
+blocked-by: 0007-folders-non-empty-confirmation
+---
+
+## What to build
+
+Make the `--yes`-confirmed merge from the prior slice collision-safe: when a
+legacy folder and its short-named target both contain an entry with the same
+name, use no-clobber move semantics so the target's existing file is never
+silently overwritten. Report which files were skipped due to a collision, and
+leave the legacy folder in place (don't remove it) whenever any collision
+occurred during that folder's migration, rather than deleting a folder that
+still holds something that couldn't be merged.
+
+This closes the gap left by the old bash `setup_folders`'s naive `mv $from/*
+$to`, which had no collision protection at all.
+
+## Acceptance criteria
+
+- [ ] A filename collision between a legacy folder and its already-populated
+      short-named target is skipped, not overwritten (the target's existing
+      file is preserved byte-for-byte)
+- [ ] The skipped collision is reported to the user
+- [ ] The legacy folder is left in place (not removed) when a collision
+      occurred, even though `--yes` was given and other non-colliding files
+      in it were moved
+- [ ] Re-running `dot setup folders` after a collision was reported and left
+      in place behaves consistently (doesn't lose the previously-skipped
+      file, doesn't re-move already-migrated files)
+- [ ] `~/.config/dot/tests/dot.fish` covers the above cases and
+      `fishtape ~/.config/dot/tests/dot.fish` passes