[Sreini]

Adds a Format namespace of media-type constants so the types accepted by
convert are discoverable via autocomplete — including JPEG XL
(image/jxl), which the API already accepts but no client surfaced.

image/jxl is already in the API allowlist (apps/api/src/schemas/optimizations.ts
and apps/opt-api/src/constants/content-types.ts), so this is a client-side
discoverability change only. There is no API-side work outstanding.

Members

WEBP, PNG, JPEG, JPG, AVIF, JXL, ANY (*/*) — mirroring the
API allowlist exactly.

Why string constants and not an enum

The JSON body has to carry the media type verbatim. A language-level enum
serializes as its name or ordinal, not image/jxl. String constants also keep
this fully backward compatible: callers passing raw strings are unaffected.

Verification

Full suite green locally: mvn test → 94 tests, 0 failures, including 3 new FormatTest cases.

Part of a coordinated change across all six Tinify client libraries, so the
same Format API is available in each.

[Sreini]

Heads-up: master itself is currently red in CI, independent of this PR.

Every Maven job now fails at POM parsing, before any compilation:

[ERROR] 'build.plugins.plugin.(groupId:artifactId)' must be unique but found
        duplicate declaration of plugin org.apache.maven.plugins:maven-dependency-plugin
        @ line 295, column 21

pom.xml declares maven-dependency-plugin twice, at line 200 and line 297. That duplicate is pre-existing on master (introduced in 897291f "Fixed transient dependencies for okhttp"); this PR does not touch pom.xml at all.

Verified with a throwaway branch at master's exact tip, zero changes (since deleted): 4 failures, 22 cancelled, 0 passes, same line 295 error.

Why now and not in September, when this PR was green across 64 checks: older Maven treated a duplicate plugin declaration as a warning, newer Maven treats it as a build error. The CI setup does not pin a Maven version, so the runner image moved underneath the repo.

Fix is to delete one of the two maven-dependency-plugin blocks. I have deliberately left it out of this PR, since it is unrelated to the Format change and affects every branch — happy to send it as its own PR if you'd like.

Locally on Maven 3.9.15 (which still only warns) the full suite passes: 94 tests, 0 failures, including the 3 FormatTest cases.