v0.3.0

Bump to 0.3.0 — Receive Share Intent (incoming share sheet target)

• flutter: add receive_sharing_intent ^1.9.0 (text/plain, image/, video/)
• dart: add PracticalReceiveShareControl listening getInitialMedia() + getMediaStream() → triggerEvent('share') with SharedMediaFile{path,type,mimeType,thumbnail}, get_initial_share/reset invoke handlers
• python: add ReceiveShare service (practical_receive_share) with on_share(files) callback, get_initial_share(), reset(), page.services auto-mount — replaces native ShareReceiverActivity via pure Flet
• example: add examples/09_receive_share.py demo (check initial share + reset)
• test: add test_receive_share + test_background_service, update README 8→9 features, modules overview §9 and examples list
• bump pyproject + flutter pubspec + __init__ to 0.3.0

flutter analyze: 0 issues, pytest 17/17 passed