Document drawButton repeat-fire semantics and local dev/test setup

[dmccoystephenson]

Summary

• README.md's drawButton bullet said the callback fires "on click", but the implementation polls mouse state on every call with no click-edge detection — it fires once per call while the mouse is held down, not once per click. Reworded the bullet and added a matching docstring on drawButton so the behavior is discoverable from an IDE.
• Added a test that holds the mouse down across several drawButton calls and asserts the callback fires once per call, pinning the documented (intentionally unchanged) behavior.
• Added a README "Development" section documenting the venv + pip install -e ".[test]" + pytest sequence, mirroring .github/workflows/test.yml, and noting the suite is headless via conftest.py.
• Added .venv/ to .gitignore since the new Development section tells contributors to create one.

No public API changes — documentation and test-only, plus a docstring.

Deferred: issue #23 (drawImage per-call re-read/re-scale caching) is a separate, non-documentation change to graphik.py and was left for a future cycle rather than batched with these README fixes.

Test plan

• python3 -m py_compile src/main/python/preponderous/graphik/graphik.py
• python3 -m pytest -q → 20 passed (19 previously + 1 new)

Closes #24
Closes #25

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

[dmccoystephenson]

Self-review rubric:

Universal:

• Scope: PASS — every changed file (.gitignore, README.md, graphik.py, test_graphik.py) is necessary for README misdescribes drawButton's callback semantics #24 or README documents no way to run the test suite locally #25; no unrelated formatting/renames.
• Tests-new: PASS — the new test test_draw_button_fires_callback_once_per_call_while_mouse_held exercises the documented repeat-fire behavior.
• Tests-fix: N/A (not a bug fix — this PR documents existing, intentionally-unchanged behavior). Sensitivity checked instead: temporarily patched drawButton to add edge-detection and re-ran the new test — it FAILED (1 == 5 assertion error), confirming it actually detects a behavior change rather than being a tautology. Reverted with git checkout -- and re-confirmed 20/20 pass.
• Sibling structure: PASS — new test follows the same style as its neighbors (uses _make_graphik, monkeypatch on pygame.mouse, matches the parametrized test right above it).
• Sibling renames: N/A — no identifier renames in this PR.
• Docs: PASS — README drawButton bullet, graphik.py docstring, and the new Development section all describe the current, verified behavior.
• Issue resolution: PASS — README misdescribes drawButton's callback semantics #24's exact concern (README wording vs. polling implementation) is fixed with matching evidence (docstring + test); README documents no way to run the test suite locally #25's exact concern (no local test-running docs) is fixed with a Development section mirroring .github/workflows/test.yml.
• Manual validation: PASS — py_compile succeeds, import smoke test succeeds, pytest → 20 passed on the PR head.

Repo-specific:

• camelCase: N/A — no new public methods added.
• Backward-compat: PASS — no existing public member's signature/behavior changed; gh search code "drawButton" org:Preponderous-Software org:Stephenson-Software shows only consumers calling it, none relying on once-per-click semantics that this PR would break (the repeat-fire behavior itself is unchanged, only documented).
• Headless: PASS — new test uses the existing conftest.py dummy SDL drivers, no real display/audio needed.
• Version sync: N/A — no version string touched.
• No new deps: PASS — no new imports; Dependencies list in README unchanged (still just pygame).

Deferred: issue #23 (drawImage caching) is left for a future cycle — it's a separate, non-documentation change to graphik.py's runtime behavior, not batched with these README-scoped fixes.

Summary: all rubric items pass; no judgment-call flags to leave inline.

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drafted by Claude on behalf of Daniel Stephenson