Split memory and task tracking docs

TODO.md

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+# TODO
+
+This file tracks the active execution queue. Use [`MEMORY.md`](./MEMORY.md) for durable context, sourced facts, guardrails, and decisions.
+
+Last updated: `2026-03-28`
+
+## Now
+
+- [ ] Implement `getRho.m` and include the required stratosphere branch for altitude `> 11 km`.
+- [ ] Fill the known assignment constants in [`code/Interceptor_3DOF.m`](./code/Interceptor_3DOF.m) and [`code/getGuidance.m`](./code/getGuidance.m).
+- [ ] Replace the current syntax-breaking `XX` placeholders that prevent the model from starting in Octave.
+
+## Blocked
+
+- [ ] Transcribe missile and target reference areas, thrust curves, mass curves, and drag tables from [`docs/Missile and Target Data for 3DOF Spring 26.pdf`](./docs/Missile%20and%20Target%20Data%20for%203DOF%20Spring%2026.pdf).
+
+## Next
+
+- [ ] Replace the remaining `XX` arrays in [`code/T3dxdt.m`](./code/T3dxdt.m) and [`code/M3dxdt.m`](./code/M3dxdt.m) with sourced data.
+- [ ] Run [`code/Interceptor_3DOF.m`](./code/Interceptor_3DOF.m) in Octave and fix the next runtime errors.
+- [ ] Verify the required plots and inspect `Ttrajectory.csv` and `Mtrajectory.csv`.
+
+## Done Criteria
+
+- [ ] No remaining `XX` placeholders in executable code.
+- [ ] `getRho.m` exists and is used by both vehicle dynamics models.
+- [ ] The atmosphere model includes the required stratosphere handling for altitude `> 11 km`.
+- [ ] The full script runs in Octave without syntax or runtime errors.
+- [ ] The required plots and CSV outputs are generated.