Add the unified AmplHeader to @ampl/kit (v0.3.0)

[juancobo]

Adds AmplHeader, the shared two-band header for every ampl.tools tool: a white institutional band (AMPL lockup + lab-site nav, owned by the kit, with full/compact sizing) and a deep-plum WORKSHOP band (cross-tool switcher, contextual nav, EN/ES, and a signed-in account chip or sign-in link), plus a hamburger mobile sheet. All tool variation flows through props.

• New AmplHeader exported from @ampl/kit/ui, with the DEFAULT_TOOLS registry and supporting types.
• New --color-accent-pale token, an on-dark LocaleSwitcher variant, and a shared sign-out helper.
• Header navigation, sign-in, and switcher strings in EN and ES (parity enforced).
• The auth front door now renders AmplHeader (full masthead).
• SiteHeader is deprecated in favour of AmplHeader but retained for backward compatibility.
• Documented in CONSUMING.md and the kit README. No database migrations. Bumps @ampl/kit to 0.3.0 (additive, minor).

[Copilot]

Pull request overview

Adds AmplHeader as the unified two-band AMPL header for the kit and wires the auth app root to use it, while preserving the deprecated SiteHeader export for compatibility.

Changes:

• Introduces the kit/ui/ampl-header component set, default tool registry, public types, mobile sheet, account menu, and shared lab navigation.
• Adds LocaleSwitcher dark variant, shared sign-out action helper, header/switcher i18n strings, and a new accent-pale theme token.
• Updates auth root rendering, docs, version metadata, and SSR tests for the new header.

Reviewed changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
app/root.tsx	Replaces the old SiteHeader composition with AmplHeader and dark locale switcher.
CONSUMING.md	Documents AmplHeader, props, usage patterns, CSP notes, and v0.3.0 release notes.
kit/README.md	Adds kit-level AmplHeader usage documentation.
kit/locales/en.ts	Adds English header, nav, and switcher strings.
kit/locales/es.ts	Adds Spanish header, nav, and switcher strings.
kit/theme.css	Adds --color-accent-pale and updates accent-deep usage comments.
kit/ui/AccountWidget.tsx	Reuses the shared sign-out URL helper.
kit/ui/LocaleSwitcher.tsx	Adds the on-dark visual variant.
kit/ui/index.ts	Exports AmplHeader, DEFAULT_TOOLS, and header types; marks SiteHeader deprecated.
kit/ui/lib/sign-out.ts	Adds shared logout form action URL builder.
kit/ui/ampl-header/AccountMenu.tsx	Adds signed-in account dropdown for the header.
kit/ui/ampl-header/AmplHeader.tsx	Adds top-level header composition and mobile sheet state.
kit/ui/ampl-header/InstitutionalBand.tsx	Adds logo/lab-nav band and mobile menu toggle.
kit/ui/ampl-header/MobileSheet.tsx	Adds hamburger-controlled mobile navigation/account sheet.
kit/ui/ampl-header/ToolSwitcher.tsx	Adds cross-tool native disclosure switcher.
kit/ui/ampl-header/WorkshopBand.tsx	Adds plum tool band with contextual nav, locale switcher, and auth controls.
kit/ui/ampl-header/index.ts	Adds barrel exports for the header module.
kit/ui/ampl-header/lab-nav.ts	Adds shared lab-site navigation link registry.
kit/ui/ampl-header/tools.ts	Adds default AMPL tool registry.
kit/ui/ampl-header/types.ts	Adds public header prop/data contracts.
package.json	Bumps package version to 0.3.0.
package-lock.json	Syncs lockfile package version.
tests/kit/AmplHeader.test.ts	Adds SSR rendering coverage for header states and variants.
tests/kit/LocaleSwitcher.test.ts	Adds coverage for default and dark locale switcher variants.
tests/routes/root-header.test.ts	Updates root header SSR tests for AmplHeader.

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