docs(optimizr): add logo and fix rtd deps

docs/source/theory/mathematical_foundations.md

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+# Mathematical Foundations
+
+This section provides formulas used across OptimizR algorithms.
+
+## Differential Evolution
+- Mutation and crossover follow classic DE/rand/1 and best/1 strategies.
+- See Storn & Price (1997) for full derivations.
+
+## MCMC
+- Metropolis-Hastings with Gaussian proposals.
+- Acceptance probability: $\alpha = \min\left(1, \frac{\pi(x')q(x\mid x')}{\pi(x)q(x'\mid x)}\right)$.
+
+## HMM
+- Baum-Welch (EM) for parameter estimation.
+- Viterbi for decoding most likely state sequence.