This PR moves coder from coder/aibridge repository into coder/coder.
It was split into 4 PRs for easier review but stacked PRs will need to be merged into this PR so all checks pass.

• chore: move aibridge library code into coder repo #24190 -> raw code copy (this PR, before merging PRs on top of it, it was just 1 commit: 70d33f3)
• chore: remove aibridge library dependency #24570 -> update imports in coder/coder to use copied code
• chore: add README, CI integration, and lint fixes #24586 -> linter fixes and CI integration (also added README.md)
• feat: exclude aibridge/fixtures directory from scripts/check_emdash.sh #24571 -> added exclude to scripts/check_emdash.sh check

Original PR message (before PR squash):
Moves coder/aibridge code into coder/coder repository.

Omitted files:

• go.mod, go.sum, .gitignore, .github/workflows/ci.yml, Makefile, LICENSE, README.md (modified README.md is added later)
• .github, example, buildinfo, scripts directories

Simple verification script (will list omitted files)

tmp=$(mktemp -d)
echo "$tmp"
git clone --depth=1 https://github.com/coder/aibridge "$tmp/aibridge"
git clone --depth=1 --branch pb/aibridge-code-move https://github.com/coder/coder "$tmp/coder"
diff -rq --exclude=.git "$tmp/aibridge" "$tmp/coder/aibridge"
# rm -rf "$tmp"