feat(scenarios): assert-based scenarios + 5 new scenarios + report comparison

[sepehr-safari]

Summary

Adds 5 new scenarios that use rich assertions (from Issue #86), bringing the total to 15 scenarios. Also adds compareScenarioReports() for regression testing.

New Scenarios

1. slow-csms-response — CSMS takes 15s to respond to BootNotification. Uses timing assertion.
2. meter-anomaly — Meter values decrease (non-monotonic). Uses payload_field and event_count assertions.
3. short-session — Session lasts 10s. Uses session_state and event_count assertions.
4. heartbeat-irregular — Heartbeats at 600s vs 300s expected. Uses event_count assertion.
5. unresponsive-csms — CSMS never responds to BootNotification. Uses failure_severity and failure_count assertions.

Report Comparison

export function compareScenarioReports(a: ScenarioEvalResult, b: ScenarioEvalResult): ScenarioComparison;

Compares two scenario evaluation results — useful for regression testing.

Files Changed

• packages/toolkit/src/scenarios/__scenarios__/slow-csms-response.ts — new
• packages/toolkit/src/scenarios/__scenarios__/meter-anomaly.ts — new
• packages/toolkit/src/scenarios/__scenarios__/short-session.ts — new
• packages/toolkit/src/scenarios/__scenarios__/heartbeat-irregular.ts — new
• packages/toolkit/src/scenarios/__scenarios__/unresponsive-csms.ts — new
• packages/toolkit/src/scenarios/compare.ts — new comparison module
• packages/toolkit/src/scenarios/compare.test.ts — 6 tests
• packages/toolkit/src/scenarios/index.ts — register 5 new scenarios + export compareScenarioReports
• packages/toolkit/src/scenarios/index.test.ts — updated for 15 scenarios + v0.3 failure codes
• tests/external-fixture/test.mjs — updated scenario count to 15
• .changeset/v03-scenarios-assertions.md — minor bump changeset
• CURRENT_STATE.md — updated with v0.3.0 progress

Closes #87

Checklist

• Scenario type extended with optional assertions field (done in feat(core): rich scenario assertions #86)
• 5 new scenarios using rich assertions
• All existing 10 scenarios still work (backward compat)
• compareScenarioReports() implemented with ScenarioComparison return type
• Unit tests for new scenarios and comparison function
• All scenario data is synthetic
• External fixture test updated
• Changeset added
• CURRENT_STATE.md updated
• Lint, typecheck, test, format all pass (365 tests)