feat: extract shared core package for web and mobile (#1006)

[VeronicDev]

Closes #1006

Summary

Extract platform-agnostic Stellar logic into a shared @stellar-dev-dashboard/core\ workspace package to eliminate duplicated code between the web app (\src/lib/stellar/) and mobile app (\mobile/src/services/stellar.ts).

Changes

New Package: \packages/core/\

• Network config (
  etworks.ts): \NETWORKS, \getServer, \getSorobanServer, \updateCustomNetworkConfig\
• Validation (\�alidation.ts): Address, amount, memo, contract, URL, network validators with \ValidationResult\ type
• Formatters (\ormatters.ts): XLM, address, stroop, instruction, byte, date, relative time formatting
• Addresses (\�ddresses.ts): Validation, parsing, SEP-29 memo check, federation resolution, universal resolver
• Reserves (
  eserves.ts): Account reserve calculations with \AccountReserves\ type
• Operation Labels (\operationLabels.ts): Human-readable labels for all Stellar operation types
• Services (\services.ts): High-level data fetching (\etchAccount, \etchTransactions, \etchNetworkStats, \etchXLMPrice) with in-memory caching
• Types (\ ypes/index.ts): Shared TypeScript interfaces

Test Suite (_tests_/)

• 7 test files covering all modules
• Tests cover primary flow, boundary cases (e.g., 7 decimal places, 28-byte memo), and failure cases (invalid inputs, network errors)

Lint Enforcement

• ESLint config with
  o-restricted-imports\ blocking React, React Native, browser globals (\window, \document, \localStorage, etc.)

Consumer Updates

• Mobile app: \mobile/src/services/stellar.ts\ now imports from core, keeps only AsyncStorage caching wrappers and \etchOperations\
• Mobile formatters: \mobile/src/utils/formatters.ts\ now re-exports from core
• Mobile types: \mobile/src/types/index.ts\ now re-exports from core
• Web app: \src/lib/stellar/networks.ts, \ormatters.ts, \�ddresses.ts,
  eserves.ts, \�alidation.ts\ now delegate to core

Workspace Config

• Added \packages/core\ to \pnpm-workspace.yaml\
• Added @stellar-dev-dashboard/core\ as workspace dependency in both \package.json\ files

Documentation

• \packages/core/README.md: Complete API reference and migration notes
• Root \README.md: Architecture section describing shared core
• \CHANGELOG.md: Feature entry for [2026 Mobile] Extract a shared core package used by both the web app and the mobile app #1006

Acceptance Criteria Met

• \packages/core\ workspace package holds platform-agnostic modules
• Both web and mobile import from @stellar-dev-dashboard/core\
• Duplicated mobile code removed
• Core has no DOM or React Native imports (enforced by lint)
• Core has its own test suite running in CI
• Automated tests cover primary flow, boundary case, failure case
• User-facing documentation updated with compatibility/migration notes

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[VeronicDev]

Kindly merge.