Build/Test Tools: Pin remaining ranged devDependencies to exact versions

[mukeshpanchal27]

Problem

.npmrc sets save-exact = true, but 15 devDependencies still carry ^ or ~ ranges.
They predate that policy.

package-lock.json is committed, so installs are reproducible today and nothing is broken.
The practical effect is that npm update moves these 15 silently while every other
dependency stays frozen — an inconsistency that will surprise whoever runs it.

Change

Pins all 15 to exact versions.

No lockfile churn

Every one of these currently resolves to the floor of its own range, verified against
package-lock.json:

Package	Was	Resolved	Now
@lodder/grunt-postcss	^3.1.1	3.1.1	3.1.1
grunt-banner	^0.6.0	0.6.0	0.6.0
grunt-contrib-clean	~2.0.1	2.0.1	2.0.1
grunt-contrib-copy	~1.0.0	1.0.0	1.0.0
grunt-contrib-cssmin	~5.0.0	5.0.0	5.0.0
grunt-contrib-imagemin	~4.0.0	4.0.0	4.0.0
grunt-contrib-uglify	~5.2.2	5.2.2	5.2.2
grunt-contrib-watch	~1.1.0	1.1.0	1.1.0
grunt-legacy-util	^2.0.2	2.0.2	2.0.2
grunt-patch-wordpress	~4.0.0	4.0.0	4.0.0
grunt-replace-lts	~1.1.0	1.1.0	1.1.0
grunt-rtlcss	~2.0.2	2.0.2	2.0.2
grunt-sass	~4.1.0	4.1.0	4.1.0
qunit	~2.26.0	2.26.0	2.26.0
sinon-test	~3.1.6	3.1.6	3.1.6

So package-lock.json is unchanged by this PR — the pins describe what is already installed.

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Draft proposal from a review of composer.json / package.json. Opened as a draft for discussion — not intended to merge as-is.