Implement the Echo Edict WIT lowerer component

[flyingrobots]

Purpose

Implement Echo's exact edict:target-provider/lowerer@1.0.0 component for the minimal generated semantic closure from #652.

Contract

The component consumes only explicit canonical Core, target-profile, semantic-closure, requested-output, and limit values from the frozen Edict WIT request. It emits canonical echo.span-ir/v1, bounded diagnostics, and only requested generated artifact roles.

Acceptance criteria

• Component bytes carry the exact digest-covered lowerer contract attestation.
• The component imports no filesystem, network, environment, clock, randomness, registry, logging callback, or WASI capability.
• Unsupported Core ABI, profile, semantic closure, operation, intrinsic, or requested role returns a typed refusal.
• Output is canonical, schema-valid, role-correct, and path-safe; the guest does not author authoritative output digests.
• The reviewed minimal fixture produces exact Target IR byte and digest parity with Edict's built-in Echo compatibility wrapper.
• Negative component fixtures cover wrong profile/domain, unsupported semantics, output overclaim, malformed output, and explicit trap.
• Repeat and cross-process invocation are equal under Edict's host limits.

Boundaries

Do not parse Edict source, resolve imports/artifacts, inspect a workspace, fetch dependencies, perform runtime execution, or silently approximate unsupported meaning.

Blocked by #651, #652, and landed flyingrobots/edict#141.
Parent: #650