chore: add structural verification checks

[CoderDeltaLAN]

Adds structural verification to the repository checks.

Scope:

• verify exactly one title;
• verify exactly one h1;
• validate JSON-LD syntax;
• detect duplicate ids;
• detect broken internal anchors;
• detect blocked claims in the landing page.

Constraints:

• README.md untouched;
• no design changes;
• no index.html changes;
• no backend;
• no secrets;
• no generated/vendor artifacts.

Local validation:

• scripts/verify.sh OK;
• git diff --check OK;
• structural integrity check OK;
• pre-push validation OK.