feat(imgproxy): add imgproxy runtime srcset builder

[dangreen]

Adds @srcset/imgproxy - runtime srcset builder for imgproxy urls.

• Imgproxy - isomorphic builder of loader-shaped srcset objects (url, src, srcSet, srcMap) for content images, e.g. from an API or a CMS; absolute integer widths, format defaults to the url path extension
• Source urls are always utf-8 base64url-encoded (the plain form needs escaping of query strings, percent and at signs, and non-ascii)
• imgproxy presets supported via the processing hook
• @srcset/imgproxy/sign - separate server-only entry with an HMAC-SHA256 url path signer (for BFF/RSC), rejects hex key/salt that Buffer.from would silently truncate
• No bundler backend by design: serving emitted originals in dev mode is not viable, so urls are built at runtime instead
• Reviewed locally with Codex: consolidated findings addressed (source url encoding, width validation, format inference, hex validation)

🤖 Generated with Claude Code

[chatgpt-codex-connector]

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[coveralls]

Coverage Report for CI Build 31254345354

Coverage increased (+0.6%) to 91.312%

Details

• Coverage increased (+0.6%) from the base build.
• Patch coverage: 58 of 58 lines across 4 files are fully covered (100%).
• 2 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

2 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
packages/loader/src/template.ts	2	90.48%

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Coverage Stats

Relevant Lines:	663
Covered Lines:	619
Line Coverage:	93.36%
Relevant Branches:	488
Covered Branches:	432
Branch Coverage:	88.52%
Branches in Coverage %:	Yes
Coverage Strength:	78713.64 hits per line

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💛 - Coveralls