fix: proofread Riemann Surfaces part

[vEnhance]

Part of the proofreading campaign (#315). This proofreads the Riemann Surfaces part, covering the six chapters under tex/riemann-surface/:

• complex-structure.tex
• morphism.tex
• affine-projective.tex
• forms.tex
• riemann-roch.tex
• line-bundles.tex

Fixes applied

Most fixes are minor (typos, subject–verb agreement, small notational slips):

complex-structure.tex

• Removed stray space before a period.
• In the complex-torus example, "complex numbers with both real and imaginary parts of $\CC$" → "parts integers" (the intended definition of $\ZZ[i]$).

morphism.tex

• Intro: "a map $f\colon\CC\to\CC$ is a morphism between Riemann surfaces" → "$f\colon X\to Y$" (the general statement).
• X put into math mode; "Some examples follows" → "follow".
• "compactfication" → "compactification".
• Multiplicity section: bullet + summary said "degree" where "multiplicity" is meant (this section defines multiplicity, not degree).
• Multiplicity proposition: stray capital $F$ → $f$ in $\phi_2\circ f\circ\phi_1^{-1}$.
• "not a Riemann manifold" → "not a Riemann surface".
• Agreement/plural fixes ("$1$-manifolds", "consists").

affine-projective.tex

• Figure label $x=2y$ → $y=2x$ (the drawn line from $(-2,-4)$ to $(2,4)$ is $y=2x$).
• "Let $f(x,y)$ a polynomial" → "be a polynomial".
• Agreement fixes ("every compact Riemann surface", "vanish", "charts are the simplest ones", "should suffice to uniquely determine").

forms.tex

• Closed an unbalanced quotation mark.
• $90 \deg$ → $90^\circ$ (matches the degree notation used elsewhere in the book).
• Agreement fixes ("take", "return", "correspond"); "we defines" → "we define".

riemann-roch.tex

• "Let $X$ be a Riemann manifold" → "Riemann surface".
• "we can add two divisors together or multiply a divisor with an integer, the result is an integer" → "and the result is again a divisor" (the result of these operations is a divisor, not an integer).
• Minor typos ("inbetween" → "in between", "we defines" → "we define", plural fixes).

line-bundles.tex

• Transition-function condition: "for each point $p \in U_1 \times U_2$" → "$p \in U_1 \cap U_2$" (the transition function lives on the overlap); scaling factor analytic on $U_1\cap U_2$.
• Isomorphism definition was circular: "isomorphic if there are line bundle isomorphisms … inverse of each other" → "line bundle morphisms".
• Agreement fixes ("make … slip", "cut out", "are simply", "smoothly vary", "look", "lines look").

⚠️ Flag: possible larger inconsistency in the "More complicated $L(-)$ spaces" example (riemann-roch.tex, lines ~89–118)

I did not rewrite this, per campaign guidance. The example introduces the space $L(-1\cdot 3 + 4\cdot i + 5\cdot\infty)$ (pole of order $\le 5$ at $\infty$), and the in-text examples on the next line confirm this bound — e.g. $(z-3)^4$ (a pole of order 4 at $\infty$) is listed as being in the set, which requires the $\infty$-bound to be $\ge 4$.

However, the dimension computation then refers to $L(-1\cdot 3 + 4\cdot i + \mathbf{3}\cdot\infty)$, maps it via $f\mapsto f\cdot(z-i)^4$ to $L(-1\cdot 3 + 7\cdot\infty)$, and concludes the dimension is 7.

These are inconsistent. For the space as actually defined ($5\cdot\infty$), the bijection lands on $L(-1\cdot 3 + 9\cdot\infty)$ — polynomials of degree $\le 9$ vanishing at $3$ — so the dimension should be 9, not 7. Either the definition (and the $(z-3)^4$ example) should use $3\cdot\infty$, or the bijection target and answer should be $9\cdot\infty$ / dimension 9. Since I couldn't determine the intended value with confidence, I left the text unchanged and am flagging it here for a maintainer.

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