fix(pkg): declare bin without a "./" prefix

[murffious]

Closes #46.

Nothing was ever removed

@npmcli/package-json/lib/normalize.js, the code that emits the warning:

const binTarget = secureAndUnixifyPath(pkg.bin[binKey])   // "./bin/rainfall.js" -> "bin/rainfall.js"
...
if (binTarget !== pkg.bin[binKey]) {
  changes?.push(`"bin[${base}]" script name ${binTarget} was invalid and removed`)
}
pkg.bin[base] = binTarget                                  // assigned, not deleted

The line after the message assigns the corrected value. The three branches that genuinely drop a bin are all above it and all say removed invalid "bin[...]" — none of them fired here.

So the message is inaccurate twice over: it says removed for what is a rewrite, and it prints the corrected path as the thing that "was invalid". That is why it never matched the declared value and read as unexplained.

The registry confirms it — 0.3.2 and 0.4.0 both published with "bin": {"rainfall": "bin/rainfall.js"} intact.

Why fix it anyway

The wording is shape-identical to the warnings that do drop a bin. Leaving it printing on every release is exactly the noise that hides a real one later — and this package has shipped three versions that could not be imported while the suite was green.

Change

• package.json: "rainfall": "bin/rainfall.js" (was "./bin/rainfall.js")
• __tests__/package.test.js: fails if any bin target regains the prefix

exports is deliberately untouched — Node's spec requires ./ there. The guard targets bin only.

Verification

Check	Result
npm publish --dry-run before	warns "bin[rainfall]" script name ... invalid and removed
npm publish --dry-run after	no warnings at all
npm pkg fix on the old manifest	changes this one line and nothing else
Isolated A/B repro (./ vs plain)	prefix is the sole cause
New test with prefix restored	fails (1 failed, 8 passed)
New test as shipped	passes (9 passed)
npm pack → install into clean project	.bin/rainfall -> ../@morf_engineering/rainfalljs/bin/rainfall.js, rainfall components runs

No version bump: the published metadata is already the normalised form, so this changes nothing for consumers. It rides the next release.

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