fix(web): address review comments in Offcanvas and dynamic color docs

[crishpeen]

Description

Addresses open PR review comments by refining Offcanvas modal/non-modal behavior ordering and cleaning up docs/demo markup.

Implemented changes:

• Offcanvas:
  • unified modal/non-modal branch ordering in show()
  • kept is-non-modal class handling consistent
  • added spacing/readability tweaks around modal conditionals
• Drawer docs demo:
  • updated heading/button capitalization to Non-modal Drawer
  • removed extra explanatory paragraph per review suggestion
• Dynamic Color playground/demo:
  • switched controls container from docs-Stack/Grid + FieldGroup wrappers to regular Stack-based fieldset layout
  • applied clearer section legends (typography-body-medium-semibold mb-900)
  • used Stack--hasIntermediateDividers for section separation
  • renamed legend to Common Formula (advanced)
  • changed reset button to type="reset" and moved reset syncing to form reset handler
  • changed static border showcase from <button> to <div> blocks

Validation performed:

• corepack yarn prettier --check on changed files
• corepack yarn workspace @alma-oss/spirit-web lint
• corepack yarn workspace @alma-oss/spirit-design-tokens build
• corepack yarn workspace @alma-oss/spirit-web test:unit -- Offcanvas.test.ts

Additional context

• This branch is layered on top of feat/dynamic-color-css-vars-playground and focuses specifically on review follow-ups.

Issue reference