Implements the Phase 1 exit-gate test from proposal/11-roadmap.md: a
nontrivial single-clock FIFO with explicit reset and const-generic
width, wired into the CIRCT round-trip CI gate alongside counter and
arbiter.

Bug-rejection corpus confirms strata-check rejects width and reset
violations (method_type_mismatch, register_reset_type_mismatch,
lowering_rejected/MissingReset). CDC is documented as a real,
currently-unimplemented gap: the checker has no domain/mem/CDC
semantics yet, so cdc_bridge.strata's body is wholesale deferred
rather than analyzed. This is expected to land in Phase 2's typed CDC
bridges with contracts, not silently faked here.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>