build(site): use npm ci and clean up docs CI pipeline

[shahar-h]

What this PR does / why we need it:

Switch the docs build from npm install to npm ci for deterministic, reproducible dependency resolution.

• Commit site/package-lock.json — removed it from site/.gitignore so the lockfile is tracked in version control.
• Use npm ci instead of npm install in docs-gen target (tools/make/docs.mk). npm ci installs exactly what's in the lockfile and fails if it's out of sync with package.json.
• Stop deleting package-lock.json in the docs.clean target, since it's now a tracked source file.
• Remove standalone Hugo setup step from CI (docs.yaml) — Hugo is already provided via the hugo-extended npm package in package.json.
• Use site/.nvmrc for Node version in CI instead of hardcoding node-version: '18'.

npm install can silently resolve different dependency versions across builds, leading to non-reproducible docs output. npm ci is faster in CI (skips dependency resolution) and guarantees the exact dependency tree from the lockfile.

Which issue(s) this PR fixes:

N/A

Release Notes: No

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[Copilot]

Pull request overview

This PR improves the docs build process by switching from npm install to npm ci for deterministic dependency resolution, commits the package-lock.json file to version control, and simplifies the CI pipeline by removing redundant Hugo setup since Hugo is already provided via the hugo-extended npm package.

Changes:

• Switch from npm install to npm ci in the docs build target for reproducible builds in CI
• Commit site/package-lock.json to version control (removed from .gitignore) to ensure exact dependency pinning
• Remove the standalone Hugo installation step from CI workflow as Hugo is provided via the hugo-extended npm package
• Use site/.nvmrc for specifying Node version in CI instead of hardcoding node-version: '18'

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
tools/make/docs.mk	Changed npm install to npm ci and removed package-lock.json deletion from clean target
site/.gitignore	Removed package-lock.json from gitignore to track lockfile in version control
site/package-lock.json	Added complete lockfile with pinned dependency versions for reproducible builds
.github/workflows/docs.yaml	Removed standalone Hugo setup step and switched to node-version-file configuration

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.32%. Comparing base (c3d06fa) to head (2ac8575).
⚠️ Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8694      +/-   ##
==========================================
- Coverage   74.34%   74.32%   -0.03%     
==========================================
  Files         244      244              
  Lines       38768    38768              
==========================================
- Hits        28824    28814      -10     
- Misses       7950     7958       +8     
- Partials     1994     1996       +2     

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