[Feature] V2: implement bonded assertion posting

[collinsezedike]

Summary

Implement v2's assert_outcome equivalent: the optimistic first stage of a v2 assertion, before any dispute exists.

What to build

A function taking (asserter: Address, outcome: bool) that:

• Requires asserter's authorization.
• Transfers the deployment's configured base_bond from asserter into the contract.
• Creates a new AssertionV2 (see [Feature] V2: implement PolicySnapshot and versioned assertion state #64) with a freshly pinned PolicySnapshotV2, status = Pending, outcome set, and no disputer yet.
• Emits an event equivalent to v1's Asserted, versioned for v2.
• Returns the new assertion id.

If the challenge window (registration_duration_secs is irrelevant here; this stage uses the same uncontested-window concept as v1) elapses with no dispute call, finalize behaves exactly as v1's does: the outcome stands, bond returns to the asserter (minus any configured finalize reward, if v2 keeps that mechanic, confirm during implementation whether v1's finalize_reward_bps carries over unchanged).

Depends on

#64 (PolicySnapshotV2 and AssertionV2 must exist first).