docs(classical-mechanics): add configuration API maps

[Robby955]

Motivation

Related to #1414, tracking maps for the configuration-space APIs in #846, #863 and #883. An API map records the implemented status and source location of each requirement for an API, so the gap between a planned API and the current library stays visible in-tree.

Changes

Adds three maps under Physlib/ClassicalMechanics/: HarmonicOscillator/Geometric/API-map.yaml, Lagrangian/API-map.yaml and Pendulum/API-map.yaml.

The harmonic-oscillator map covers the geometric configuration-space development that exists (ConfigurationSpace, its manifold structure, the coordinate homeomorphism and diffeomorphism, trajectories and kinetic energy). The pendulum map marks the sliding-pendulum pieces that exist and leaves the manifold structure, the map to Space, trajectories and the lagrangian as not done. The general configuration-space map enumerates the per-system state of the library, with the double-pendulum stub marked not done.

References cite Landau and Lifshitz, Mechanics, 3rd ed., Chapter 1.

Testing

Ran the API-map linter:

python3 scripts/api_map_linter.py --repo .

Every declared source file and name resolves; no completed entry is missing a location.

[github-actions]

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