chore(docs,ci,build): utils integration + Polkadot stable2503 alignment

[WRRicht3r]

• Summary: Improve contributor workflow and align the wallet with the
  Polkadot SDK polkadot-stable2503 by adding runtime override hooks and enabling
  development against a local fearless-utils-Android checkout.

• Changes:

  • AGENTS.md: New contributor guide tailored to this repo (structure,
    commands, style, testing, PRs).
  • runtime/build.gradle: Added env/local.properties overrides for TYPES_URL,
    DEFAULT_V13_TYPES_URL, and CHAINS_URL to match specific SDK releases (e.g.,
    stable2503).
  • settings.gradle: Composite build include for local fearless-utils-Android
    via FEARLESS_UTILS_PATH (fallback to /Users/williamrichter/Git/
    fearless-utils-Android) with explicit dependency substitution.
  • scripts/validate-local.sh: Helper to verify JDK/SDK and run detekt/tests/
    lint.
  • .github/workflows/android-ci.yml: CI for detektAll, runTest (unit tests +
    JaCoCo), and :app:lint on PRs/pushes.
  • .github/pull_request_template.md and issue templates: Standardize
    submissions.
  • README.md and CONTRIBUTING.md: Added CI badge, local validation, utils
    usage, and cross-links to AGENTS.md.

• How to use:

  • Local utils: export FEARLESS_UTILS_PATH=/absolute/path/to/
    fearless-utils-Android; then ./gradlew :app:assembleDebug or bash scripts/
    validate-local.sh.
  • Pin to polkadot-stable2503-compatible registries via env or
    local.properties:
    • TYPES_URL_OVERRIDE=…
    • DEFAULT_V13_TYPES_URL_OVERRIDE=…
    • CHAINS_URL_OVERRIDE=…

• Notes:

  • Building local utils requires NDK 25.2.9519653 and Rust (rustup/cargo).
  • Composite build only affects local dev; CI uses published artifacts.

• Checklist:

  • detektAll, runTest, and :app:lint pass
  • No secrets/local.properties committed
  • If bumping shared_features, verify metadata decoding and basic flows
    (balances, transfer, XCM) against a stable2503 node