feat(util): RFD R2+R4+R5 — surface precision marker + soundness check + live unsound detection

[Disentinel]

Stacked on R1 (#462). Consumes the precision marker. TS-only (util + mcp); no rust/.dl/SCIP/guarantees.yaml.

• R5 — traceEffects surfaces suspected_unsound[] + per-leaf precision: a member call whose receiver IS a non-relative import but resolved to a PURE ecma-GLOBAL::method (the axios.get→GLOBAL::get defect) is explicitly marked unsound (complementary to PART A fix(util): propagate effects-db effects through member calls on default-imported modules (SEP PART A) #460's effect-recovery).
• R2 — precision class + candidateCount thread additively into find_calls (CallInfo.precision), the traceEffects result, and the MCP describe/trace-effects surfaces.
• R4 — soundnessOf (precise | sound-superset | unsound) + checkResolutionSoundness(backend) hard-flags unsound resolutions as violations, even though they pass the ≤1-target is-a-function guarantee.

Verify (live /tmp/sep-test)

checkResolutionSoundness: hasUnsound=true  bySoundness={sound:1, sound-superset:3, unsound:1}
  violation: axios.get → GLOBAL::get  receiverModule=axios  basis=imported-default-method-to-ecma-global  verdict=unsound
traceEffects(fetchUser).suspected_unsound: [{ call_name:"axios.get", resolved_to:"GLOBAL::get", receiver_module:"axios" }]

Tests: ResolutionPrecisionConsumers (7) + R1 + trace-effects = 28/0; findCallsInFunction 26/0; ContextCommand 10/0.

Merge order (3-PR stack touching traceEffects.ts)

Merge #462 (R1) + #460 (PART A effect-recovery) to main first, then rebase this branch onto main (reconcile the processTarget receiver path — PART A recovers effects, R5 adds the unsound mark; complementary). After both land, a consumer sees BOTH the recovered IO:HTTP:REQUEST and the suspected-unsound flag.

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