doc: add theorem 8 (straightedge-and-compass construction) to 100.yaml

[wwylele]

Adding my repo as an external proof to the theorems.

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A hard part of these theorems is verifying the definition and the statement. I have extracted the relevant definition in the Challenge.lean file for review. This is also verifiable using comparator. I followed wikipedia for the definition of constructibility

Zulip thread: #general > The impossibility of trisecting the angle (there is discussion about whether this definition allows "picking an arbitrary point")

I plan to upstream some or all of the project, but I anticipate it to be a long process, and it is not clear to me whether the entire project is within the scope of Mathlib, which is why I am only adding a link to the repo for now

AI usage disclosure: this 63 lines were generated by Aristotle. The rest were written by me.

[github-actions]

PR summary 8c70e8e5bd

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff (regex)

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

✅ Lean-aware diff — post-build, computed from the Lean environment (commit 8c70e8e).

• +0 new declarations
• −0 removed declarations

No declaration differences.

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No changes to strong technical debt.

No changes to weak technical debt.

Current commit 8c70e8e5bd
Reference commit f98b1aa39a

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/technical-debt-metrics.sh pr_summary

• The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
• The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).