Task 377: Add Trim-Thrust Profile Chart to EP02

Status: DONE

Motivation

EP02 had only 1 timeseries chart (velocity profile), the fewest of any episode:

• EP01: 2 charts (mass-transit-time, velocity-profile)
• EP02: 1 chart (velocity-profile) ← gap
• EP03: 2 charts (velocity-profile, thrust-profile)
• EP04: 3 charts (radiation-dose, shield-life, thrust-comparison)
• EP05: 4 charts (velocity-profile, nozzle-life, thrust-profile, acceleration-evolution)

Changes

1. EP02 thrust profile chart (ep02-chart-thrust-profile):

- Shows 2-phase trim-thrust operation: 3d accel → ~101d coast → 3d decel (107 days total)

- Primary series: 0.098 MN (1% of 9.8 MN) with ±10% error bands (0.088-0.108 MN)

- Comparison series: accel-only model (3d+0d, dashed red) — shows the v∞ problem scenario

- Annotations: phase labels for acceleration, coast, and deceleration

- Threshold line: trim thrust reference level

1. TDD tests in article-content-validation.test.ts:

- Chart presence test (ep02-chart-thrust-profile)

- Thrust level verification (0.098 MN)

- 2-phase vs accel-only model comparison

Total: +3 new content validation tests. All 2,522 TS tests pass, 398 Rust tests pass.