Implement E2E tests for the Fellowship salary pallet

[rockbmb]

Summary

E2E test suite for the Fellowship salary pallet on Polkadot Collectives (post-Hollar migration).

Tests

• Full salary lifecycle: induct → register → payout, verifying claimant state transitions and XCM dispatch
• Cycle status invariants: budget reset on bump, totalRegistrations accumulation after register, totalUnregisteredPaid tracking
• Cross-chain payment: payoutOther delivers Hollar to an explicit beneficiary on Asset Hub via XCM
• Unregistered payout: fellow who missed registration receives payment from the residual budget pot
• Proration: payouts scale down when total registrations exceed cycle budget
• isSufficient dependency: payout XCM fails silently when recipient has no DOT on Asset Hub (Hollar is not a sufficient asset)
• Mid-cycle promotion: payout uses the registered amount (rank at registration), not the member's current rank after promotion

All salary amounts and period lengths are read from live chain state (fellowshipCore.params, fellowshipSalary constants). Prerequisite state (collective membership, claimant status) is seeded via setStorage; the extrinsic under test is always exercised for real.

Closes #642

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