feat(emv2): error-propagation traversal across AADL connection graph (v0.10.x)

[avrabe]

Summary

• Closes the single biggest gap vs OSATE/HAMR: EMV2 error-propagation traversal now walks the AADL semantic connection graph to compute which downstream components inherit each declared error type (structural fault tree + cut sets were already present)
• New emv2_propagation.rs module: Emv2Overlay carries in/out propagation and flow declarations; compute_error_propagation returns ErrorPropagationReport with chains, local flows, and diagnostics; analysis only, no codegen
• Wired into register_all / register_all_except_wctt; adds REQ-EMV2-PROPAGATION-001 + TEST-EMV2-PROPAGATION to artifact YAML files

Example chain from test fixture

Single-hop test (emv2_propagation_single_hop): component sensor (Device) declares out propagation { BadValue }, component controller (Process) declares in propagation { BadValue }, one semantic connection between them. Result:

ErrorPropagationChain {
    origin: sensor,
    error_type: "BadValue",
    downstream: [controller],
    via_connections: [c_0_1],
}

Test plan

• cargo test -p spar-analysis emv2_propagation — 6 tests pass (single-hop, 3-hop chain, cycle detection, path-flow isolation, case-insensitive match, no-connection baseline)
• cargo clippy -p spar-analysis -- -D warnings — clean
• cargo fmt --check — clean
• rivet validate — YAML parse error at line 1615 of verification.yaml is pre-existing (confirmed against main), not introduced by this PR

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