Fix broken links to renamed repos and trailing-slash URL

[adivx]

Summary

Fixes three broken links:

1. odp/cli/configuration.md — linked to /odp/python/extensions/ with a trailing slash (404 on docs.openbb.co). Removed the trailing slash.

2. workspace/developers/widget-parameters/input-form.md — the "Form Example" linked to backend-examples-for-openbb-workspace/tree/main/advanced_examples/form_parameter, which returns 404. The repo was renamed to backends-for-openbb and the example moved to widget-examples/parameters-types/form_parameter. Updated to the working path.

3. workspace/developers/ai-features/citations-for-documents.md — linked to agents-for-openbb/tree/main/vanilla-agent-pdf-citations, which returns 404. The example is now at 36-vanilla-agent-pdf-citations. Updated.

Verification

• docs.openbb.co/odp/python/extensions/ → 404 → /odp/python/extensions → 200
• github.com/OpenBB-finance/backend-examples-for-openbb-workspace/.../advanced_examples/form_parameter → 404 → github.com/OpenBB-finance/backends-for-openbb/.../widget-examples/parameters-types/form_parameter → 200
• github.com/OpenBB-finance/agents-for-openbb/tree/main/vanilla-agent-pdf-citations → 404 → .../36-vanilla-agent-pdf-citations → 200

Not fixed here (may need maintainer guidance)

• agents/app-builder-resources.md links to github.com/OpenBB-finance/workspace-mcp, which appears to be deleted with no replacement in the org.
• openbb.co/request-a-feature, openbb.co/schedule-demo, openbb.co/use-cases/data-vendors are all 404; the site has restructured (e.g. /contact exists) but no direct equivalent was obvious.