ci(l1,l2): avoid running L1 and L2 workflows on docs editing

[lferrigno]

Avoid running L1 and L2 workflows on docs editing

[Copilot]

Pull Request Overview

Avoid running L1/L2 CI workflows for documentation-only changes and add a new documentation page for recommended lectures.

• Add Recommended lectures page and link it in the docs sidebar.
• Update L2 (TDX build and prover) and L1 PR workflows to ignore docs changes.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/SUMMARY.md	Adds a sidebar link to the new Recommended lectures page.
docs/LECTURES.md	Introduces a new docs page with curated lecture links.
.github/workflows/pr-main_l2_tdx_build.yaml	Skips workflow on PRs that only change files under docs/**.
.github/workflows/pr-main_l2_prover.yaml	Skips workflow on PRs that only change files under docs/**.
.github/workflows/pr-main_l1.yaml	Skips workflow on PRs that only change files under docs/**.

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[Copilot]

Docs-only commits pushed to main will still trigger this workflow because paths-ignore is only configured for pull_request. To fully avoid running on documentation-only edits, also add paths-ignore under push.

[Copilot]

Docs-only commits pushed to main will still trigger this workflow because paths-ignore is only configured for pull_request. Mirror the ignore rule under push to prevent unnecessary runs on documentation-only changes.