chore: drop the unproduced coverage badge, ignore .DS_Store

[OmarAlJarrah]

Summary

Two README/.gitignore hygiene problems, both cases of the shared files carrying a claim or an
entry that nothing in this project backs.

The coverage badge is removed rather than generated. README.md:16 was a literal
img.shields.io/badge/coverage-100%25-success.svg with the value baked into the URL path. Nothing
computes it: .github/ contains exactly one file, workflows/gate.yml, and it has no coverage
upload, gist write, or badge action — its coverage step runs scripts/check-coverage.sh, which
prints and exits. So the badge asserted 100% unconditionally and could not go red, which is the
worst property a badge can have.

Of the two honest options — publish the number from CI, or drop it — dropping it is the better
trade here:

• The live workflow badge on the line above (README.md:13) already carries the signal.
  coverage is a required step of the single gate job, so a coverage regression fails the job
  and turns that badge red. A generated shields badge would report the same one bit through extra
  machinery (a gist plus a token, or a third-party action) that the repo does not have today.
• There is no interesting number to publish. Coverage here is a binary gate at exactly 100%, not a
  trend line — check-coverage.sh fails the build on one uncovered statement. A badge reading
  "100%" is only ever restating "the build passed".
• CLAUDE.md already settles the general case: derive counts, never maintain them, and if a claim
  about code must be written down, name the revision it was true at. A hardcoded badge is a
  maintained count with no revision attached.

The MIT and Go-version badges stay. MIT is immutable; the go-1.26 badge is a version claim that
floats with the toolchain pin and is being handled under #61, so it is deliberately untouched here.

.gitignore now lists only what this project produces. Removed four per-contributor tooling
paths — .superpowers/, docs/superpowers/, .claude/, .crush/. None has ever appeared in a
commit (git log --all -- <path> is empty for all four), and docs/superpowers/ was explicitly
untracked in 0b69247 chore: stop tracking local SDD planning docs precisely because those files
are local, which is the argument for keeping the rule per-clone rather than shared. Contributors
who run any of that tooling should put these in .git/info/exclude or a global
core.excludesFile:

printf '%s\n' .superpowers/ docs/superpowers/ .claude/ .crush/ >> .git/info/exclude

Added .DS_Store, which was untracked and unmatched by any rule in a repo developed on macOS —
it sits in the working copy right now and would be committed by accident before any of the entries
above caused trouble. .idea/ and .vscode/ were already ignored, so the omission was an
inconsistency rather than a policy. Nothing else is missing: cover.out is covered by *.out, the
CLI binary by /morphic, verify-atomic-output.sh works in mktemp -d outside the tree, and
go build ./... leaves no binaries behind (verified). No speculative entries were added for
platforms or tools this repo shows no evidence of.

/out.json, /logs.txt and /pets.json are kept. They are repo-root scratch outputs of real CLI
runs and #11 settled that they belong in the shared file.

Ordering. README.md is also being rewritten by #315, which reworks the Building and Testing
sections. This change touches only the badge block at the top, which #315 does not, so the two
merge cleanly in either order. The related "overall and per package" coverage claim further down
the README is already corrected by #315 and is left alone here to avoid a conflict. gate.yml is
untouched for the same reason — that file has other changes in flight, and dropping the badge needs
nothing from CI.

Test plan

• git check-ignore -v .DS_Store exits 0 (.gitignore:36) where it exited 1 before, and
  git status --porcelain no longer lists ?? .DS_Store. Deleting just that one line restores
  both failures, confirming the rule is what does the work.
• git check-ignore on the four removed paths reports not-ignored from the tracked file, and
  resolves from .git/info/exclude once migrated there.
• grep -rn 'badge\|shields' README.md docs/ returns only the gate, MIT and Go badges — no
  remaining reference to the coverage badge anywhere in the docs.
• Full gate green: gofmt, go vet, golangci-lint run, go build ./...,
  scripts/check-coverage.sh (all 4942 statements covered). No Go code changed.

Closes #91