fix: proofread Algebraic Geometry I part

[vEnhance]

Proofreading pass over the Algebraic Geometry I: Classical Varieties part (issue #315), covering tex/alg-geom/{affine-var,zariski,proj-var,bezout,quasi-proj}.tex.

Mathematical corrections

• bezout.tex: The Hilbert function of the parabola $\CC[x,y,z]/(zy-x^2)$ was stated as $2d-1$, but the listed values are $h(0)=1$, $h(1)=3$, $h(2)=5$, and the decomposition $\CC[y,z]\oplus x\CC[y,z]$ gives $(d+1)+d = 2d+1$. Corrected to $2d+1$.
• bezout.tex: The geometric moral of Bézout's theorem called $\VV(f)$ (for $f$ of degree $k$) a "hyperplane of degree $k$". A hyperplane has degree $1$; this should be hypersurface.
• proj-var.tex: $\CP^n$ is described as lines through the origin in $\CC^n$; it should be $\CC^{n+1}$ (as stated correctly elsewhere in the chapter, and consistent with the $\Aff^{n+1}$ used in the surrounding proof).
• quasi-proj.tex: The pullback $f^\sharp\varphi$ was written with codomain $Y\setminus{25}$; a regular function maps to $\CC$. Also, the pullback of $\pi_1$ is the composite $\pi_1 \circ f$ (apply $f$ first), not $f\circ\pi_1$ — fixed in two places.
• affine-var.tex: For irreducible $f$, $\VV(f)$ was called a "degree one curve"; the polynomial $y-x^2$ has degree $2$, and what is meant is codimension one.

Minor fixes

• proj-var.tex: stray $F$ → $f$; "no longer correspond" → "corresponds".
• bezout.tex: missing \cap in $h_{I_1\cap\dots\cap I_{m-1}}$; removed a garbled fragment (so and $c_{\text{new}} = \deg I+(f)$ then) in the Bézout solution; "the Pascal's theorem" → "Pascal's theorem".
• affine-var.tex: "corresponding to be" → "corresponding to"; "topology along" → "topology alone".
• zariski.tex: "difference than" → "difference from"; "a accurate" → "an accurate"; "call ... as the" / "they maps" → "call ... the" / "they map".
• quasi-proj.tex: "It what follows" → "In what follows"; "complete settles" → "completely settles"; article agreement ("an quasi-projective" → "a", "a affine" → "an", "a irreducible" → "an").

No large mathematical rewrites were needed; all changes are typo/grammar/notation-level corrections.

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