fix(ah-staking): stall detection grace period, MinerPages fix, and simulation tools

- Add 3-session grace period to stall detection to allow RC XCM round-trip
  before triggering era recovery (StallDetectionCount storage added)
- Fix plan_new_era() to always increment CurrentEra regardless of
  ElectionProvider::start() result, preventing infinite retry loops
- Fix MinerPages from 2 to 32 to match Pages config (was causing
  incomplete OCW solutions and election failures)
- Bump AH spec_version to 1_020_007
- Add subxt example scripts for simulation and mainnet operations
- Remove obsolete fix_force_era.rs (replaced by sim_reset_election.rs)

.gitignore

@@ -3,6 +3,7 @@
 .direnv/
 .DS_Store
 .env*
+chainspecs/bootnode-key
 .idea
 .local
 .lycheecache