build(deps): move styled-components to peerDependencies (CUI-37)

[JeanMarcMilletScality]

What

Move styled-components from dependencies to peerDependencies (matching react/react-dom), and add it to devDependencies so core-ui's own build/test/Storybook still resolve it.

Why

As a regular dependency, npm was free to install a nested node_modules/@scality/core-ui/node_modules/styled-components in workspace consumers. That second instance yields two ThemeProvider contexts, so useTheme() returns undefined at test/build time — this broke identity-ui's Jest run (140 failures from Checkbox/theme consumers).

Making it a peer guarantees a single hoisted instance provided by the consumer, exactly as react already works.

No Module Federation impact

The MF singleton version is negotiated from each consumer's rspack shared config (requiredVersion: deps['styled-components'], read from the consumer's own package.json), independent of core-ui's dependency classification. Runtime behavior is unchanged; this only affects install/build/test-time npm resolution.

Why the devDependencies entry is required

Peer deps of the root package are not auto-installed for the package's own dev build. react survives peer-only here only because Storybook/testing-library pull it in transitively — nothing pulls styled-components, so tsc fails without the explicit devDep. Verified: peer-only → build fails across ~40 files; with devDep → clean.

Verification

• core-ui: npm run build clean, npm test → 43 suites / 428 tests pass.
• Pilots repointed at this branch (fresh --legacy-peer-deps install, cache-clean) — all confirm a single deduped styled-components@6.4.4, no nested copy:
  • shell-ui: 92/92 pass
  • metalk8s ui: 220 pass / 2 skip / 3 todo
  • identity-ui: 248 pass (2 pre-existing GroupsTab form-logic failures, unrelated — this commit changes only package metadata, not compiled code)

🤖 Generated with Claude Code

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