docs: add the setup-srcset and srcset-cli skills

[dangreen]

Two shareable agent skills under skills/, in the format of the ones in simple-release, scripts and conventional-changelog.

setup-srcset — adding srcset to a project. Picking the integration (Vite plugin, Webpack/Rspack loader, cli baking, or a runtime proxy adapter), installing, both bundler configs, the semantics of the rules, the ambient client.d.ts types, rendering through @srcset/runtime or the framework components, the import query, placeholders, a verification checklist and the pitfalls.

srcset-cli — driving the cli, baking included. The flag table, the config file and what still needs one, all four --module layouts with a sample generated module, what the consuming project has to provide (an asset loader, sideEffects, a .d.ts for js modules), recipes and the pitfalls.

Every claim was checked against the sources, and everything runnable was run: all six recipes, every --module layout, the placeholder and select flags. Some of what the checking turned up went into the skills as warnings, since an agent would otherwise walk into it:

• an image no rule matched still produces a module in the bundler integrations — an empty one, and the page silently renders nothing;
• a raster-only format drops an svg silently, and the Vite plugin does not process .svg imports at all;
• imports inside a baked ts module need ambient declarations, which vite/client provides and a webpack project does not.

Merge after #30 — the cli skill documents the --placeholder and --select-* flags it adds.

[coveralls]

Coverage Report for CI Build 33515278068

Coverage remained the same at 93.692%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	875
Covered Lines:	828
Line Coverage:	94.63%
Relevant Branches:	631
Covered Branches:	583
Branch Coverage:	92.39%
Branches in Coverage %:	Yes
Coverage Strength:	80716.11 hits per line

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💛 - Coveralls