Resolve all StructArmed findings before 1.0.0

[roxblnfk]

The advisory StructArmed guard added in #329 reports architecture violations without failing CI. Before 1.0.0 the codebase should be clean, so the guard can be flipped to blocking.

Reproduce:

composer bin structarmed install
composer structarmed

Findings as of #329 (186 total):

• Declare @api or @internal on every class — 134 (Core 33, Bridges 37, Plugins 64)
• Annotate classes under an Internal namespace with @internal — 8 (Core 2, Plugins 6)
• Stop using another package's Internal namespace from outside it — 16 (Core 9, Plugins 5, Bridges 2)
• Stop leaking Internal types into public signatures — 3 (Plugins)
• Fix the Core -> Plugins dependency direction — 25

Once all are resolved, drop continue-on-error from the workflow so violations block the pipeline.