Add Format enum and typed exception subclasses - #22

Two BC-relevant cleanups from #4 packaged together — both are small enough to share a PR and both close BC windows that would be expensive to retrofit in 2.x.

Format enum

Same pattern as Driver / Position / FlipDirection. The convert operation was the last place magic strings leaked into the public API.

use PhpCollective\Infrastructure\Storage\Processor\Image\Format;

$variant->convert(Format::Webp);                  // typed (preferred)
$variant->convert($config['format'] ?? 'webp');   // string fallback

ImageVariant::convert() and the registry's convert factory both accept Format|string. Format::fromName() recognises the obvious aliases (jpg → Jpeg, tif → Tiff, pjpeg → Pjpg, heif → Heic, j2k / jp2k → Jp2) so existing config-driven setups with non-canonical names keep resolving.

Typed exception subclasses

Three new classes, all extending ImageProcessingException so callers can settle on a uniform catch (ImageProcessingException $e):

The decode wrap is the meaningful one — process() now catches anything intervention raises during decodePath() and rethrows as ImageCorruptedException carrying the underlying exception as previous. Apps catching truncated uploads / wrong-extension files / unsupported codecs no longer need to know intervention's exception class names.

Why ship both now

Magic-string convert(string) and raw exception types are both structural signatures — tightening them later means widening user code's catch blocks and method signatures. 2.0 is the only cheap moment to flip them; deferring would mean either dragging the magic strings into 2.x permanently or shipping another major.

Verification

• vendor/bin/phpunit — 82 tests, 227 assertions, all passing
• vendor/bin/phpstan analyze — no errors
• vendor/bin/phpcs -s — no errors
• Branch on top of latest master, no conflicts
• Diff: 4 new files (Format enum + 3 exceptions), 4 new tests, 8 touched files; +350 / -23

CHANGELOG / docs

• CHANGELOG 2.0 entry: Format added to the enum list, exception subclasses listed under Added, exception-hierarchy shifts called out under Breaking
• readme.md: convert(Format::Webp) in the Quick Example
• docs/Available-Operations.md: convert(Format|string $format) section refreshed with both call styles