Remove vestigial .gitignore entry, add CI status badge to README

[dmccoystephenson]

Summary

• A target entry is removed from .gitignore; it dated from the pre-pyproject.toml Maven-style build and no longer corresponds to any build output produced by the current setuptools-based packaging.
• A CI status badge for .github/workflows/test.yml is added to the top of README.md, since a working test workflow already exists but was not surfaced anywhere in the README.

No tracking issue — this gap was found during triage; the repository currently has no open issues or PRs.

Test plan

• python3 -m py_compile src/main/python/preponderous/graphik/graphik.py — succeeds
• python3 -m pytest (headless via conftest's SDL_VIDEODRIVER=dummy) — 25 passed
• Import smoke test (import preponderous.graphik as g; print(g.__version__)) — succeeds, prints 0.2.0
• No source or test files were touched; behavior is unchanged

This PR description was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

[dmccoystephenson]

Self-review rubric (posted per the dev-loop skill; not a formal GitHub Review object, since that API is unavailable in this dispatch):

• Manual validation: PASS — python3 -m py_compile src/main/python/preponderous/graphik/graphik.py succeeds; python3 -m pytest (headless, 25 tests) passes; the import smoke test (import preponderous.graphik as g; print(g.__version__)) prints 0.2.0. All three were re-run on the PR head after the last commit.
• Scope: PASS — only .gitignore and README.md are touched, and each hunk maps directly to one of the two summary bullets; no source or test file is modified.
• Tests-new: N/A — no public method is added, changed, or removed, so no new test is required.
• Tests-fix: N/A — no bug fix is included in this PR.
• Sibling structure / sibling renames: N/A — no new file is created and no identifier is renamed.
• Docs (Phase 7 table): PASS — README.md's Dependencies list, public-method list, and version reference are unchanged and were re-checked against graphik.py and _version.py; pyproject.toml's version is unaffected.
• Issue resolution: N/A — no Closes #N is claimed; the PR body states no tracking issue exists, since the gap was found during triage against a currently-empty issue backlog.
• camelCase / Backward-compat / Headless / Version sync / No new deps: N/A or PASS — the public Graphik surface is untouched, no test is added or removed, no version string changes, and no import beyond pygame is introduced.

path:line — finding, for the two changed hunks:

• .gitignore:1 — the removed target line is confirmed unreferenced anywhere in pyproject.toml, the GitHub Actions workflows, or RELEASING.md; it is traced via git log to a point in history that predates the pyproject.toml migration in PR Add pyproject.toml and consolidate to a single version source #6, back when a Maven-style pom.xml build was in use (no pom.xml exists in the tree today).
• README.md:2 — the added badge URL is checked against the actual workflow file name (.github/workflows/test.yml) and job name (Test); GitHub's badge endpoint convention (actions/workflows/<file>/badge.svg) is followed exactly.

Overall: a small, low-risk documentation/config cleanup with no behavioral change. Green across the board; no FAIL items are found.

This comment was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).