[BashMan11]

Summary

Extracts every user-visible string out of components/layout/navbar.tsx and into a new lib/copy/navigation.ts module exporting navigationCopy.

This follows the established copy-module pattern used by lib/copy/dashboard.ts and lib/copy/streams.ts: a plain object export with a leading comment describing the component it serves, keeping the Navbar's strings in one place as a step toward i18n-readiness.

What moved

• Nav link labels (Dashboard, Streams, Analytics, Settings)
• Offline badge tooltip/title and label
• "New stream" button label and its disabled aria-label
• Network selector labels and dropdown items (Mainnet / Testnet)
• Theme menu sr-only label and items (Toggle theme, Light, Dark, System)
• Network-mismatch banner text (split into before / switchTo / after fragments so the existing <strong> markup and rendered wording are preserved)

Notes

• UI wording is unchanged. All strings were moved verbatim; only their location changed.
• Non-visible strings (classNames, data-testid, href/src paths, object keys, enum values, comments) were intentionally left in place.
• Minimal diff: no component restructuring beyond replacing literals with navigationCopy references.
• npm run typecheck reports no errors in the changed files. (One pre-existing, unrelated error remains in components/streams/dashboard-stats.stories.tsx.)

Closes #953