feat: implement Toolbar component

[k0ndee]

Motivation

Introduce a new Toolbar component implementing the Material Design 3 toolbars spec. Reuse theme tokens (shape, color roles, elevation) and follow the same component-tokens pattern as FAB / Checkbox.

Spec re-check (M3 toolbars)

Re-checked the M3 toolbars specs:

• Two variants: floating (self-positioned pill, corner.full, elevation level 3) and docked (full-width bar pinned to the bottom edge, corner.none, no elevation, extends into safe-area insets).
• floating supports horizontal/vertical orientation; docked is always horizontal per spec.
• Default (standard) colors: container/unselected-button surfaceContainer, icon/label onSurfaceVariant, selected button secondaryContainer with onSecondaryFixedVariant (light) / onSecondaryContainer (dark) icon.
• vibrant colorScheme: container/unselected-button primaryContainer, icon/label onPrimaryFixedVariant (light) / onPrimaryContainer (dark), selected button falls back to surfaceContainer with onSurface icon.
• Direct IconButton/Button children are auto-recolored to match colorScheme unless they already set their own color (a mode on either opts them out in favor of their own mode-based coloring).

Changes

Toolbar / tokens / utils

• New src/components/Toolbar/{Toolbar.tsx,tokens.ts,utils.ts}: variant (floating/docked), orientation (horizontal/vertical, floating-only), colorScheme (standard/vibrant), containerColor override, style/contentContainerStyle, testID, aria-label, theme, ref
• Container shape/elevation/spacing resolved from ToolbarTokens; docked extends into safe-area insets via margin outside Surface's box, keeping the 64dp icon band untouched
• withToolbarChildColors auto-recolors mode-less IconButton/Button children per colorScheme, without touching children that already set their own color/mode
• Exported from src/index.tsx

Example / docs / tests

• Example screen (ToolbarExample.tsx) covering both variants, both orientations, both color schemes, over a scrollable list
• Docs page + prop table + theme colors table; screenshots for floating (horizontal/vertical) and docked, each in standard/vibrant
• Unit tests (Toolbar.test.tsx) covering shape/elevation per variant, color resolution across light/dark themes for both color schemes, and child auto-recoloring behavior

Scope note

Per Satyajit Sahoo's recommendation, this implementation is split into a series of PRs for easier review, rather than landing as one large change. This PR is PR 1 of the series:

• PR 1 (this PR) — Floating + docked variant, static (without animation, no FAB pairing), colorScheme standard/vibrant. Component, tokens, tests, docs, example.
• PR 2 — Show/hide animation (offscreen slide + spring), generic scroll shared-value primitive.
• PR 3 — FAB pairing, FAB/key-action collapse on scroll.
• PR 4 — Trailing-edge overflow menu.

Related issue

Related to #4988

Test plan

• yarn typecheck / yarn lint / Toolbar unit tests
• Full unit test suite green
• Manually verified in the example app: floating (horizontal/vertical) and docked, standard/vibrant, over scrolling content, light and dark themes

Visual verification

	standard	vibrant
floating, horizontal
floating, vertical
docked

Docs screenshots: docs/public/screenshots/toolbar_*.png.