feat(components): shared Heading Twig component for H1-H6

[martinydeAI]

Resume

Description

Several templates (templates/security/login.html.twig,
templates/profile/show.html.twig, templates/profile/edit.html.twig,
templates/components/Hero.html.twig, templates/assistant/show.html.twig)
all hand-roll the same <h1> markup with font-display text-[clamp(...)] font-medium leading-tight tracking-tight text-ink
classes. Extract a shared Heading Twig component that picks the
right HTML tag (h1–h6) from a prop and centralises the design
tokens.

Tasks

• Add templates/components/Heading.html.twig accepting a
  level prop (1–6) and rendering the corresponding tag.
• Support size/variant props if call-sites need more than one
  visual treatment (e.g. hero vs. section heading).
• Refactor existing call-sites to use the component.

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Details - AI specificities

• Raised on PR feat(profile): self-service profile show + edit (#13) #89 review.
• Existing duplicated markup: see the templates listed above.
• Keep Tailwind classes co-located in the component so the design
  tokens have a single source of truth.
• Components live under templates/components/ and are invoked via
  <twig:Name ...> (Twig Components bundle).