docs: add small-claims process profile (formula split, no arbiter)

[iret77]

What & why

Tenth PR of the v0.3 draft (maintainer decision: include a minimal small-claims profile in v0.3; the single-juror variant waits for v0.4).

Issue #21 — the dispute path was uneconomical for exactly the micro-value cases the protocol targets: §1.3 advertises near-zero-cost determinations, §7.3's own example escrows 0.50 — but arbiter fees plus two mandatory bonds dwarf that, and §10.3 lets arbiters decline underfunded Threads. Micro-value Threads had anchored evidence and silently no recourse.

New OPTIONAL urn:anp:dispute:small-claims-v1 (§9.4):

• Selection: RECOMMENDED whenever escrow value cannot cover the §9.4 bond floor + a realistic arbiter fee. Clause requires only challenge_window + a pre-agreed split formula (e.g. 50/50, or full refund).
• Happy path unchanged — assert → window → uncontested enforce; mutual settlement (M9) applies as everywhere.
• Disputed path = formula, not forum: a valid dispute triggers the pre-agreed split via the new basis: "formula_split" (§6.2.1 fourth enforcement path). The escrow contract verifies the directive against the formula recorded in escrow.open's conditions at funding time — the parties pre-consented in the accepted head; no arbiter, no evidence phase, no appeal. Trustlessly checkable on-chain with the machinery already in place (§6.2.1/§13: Uncontested enforcement requires contract-readable anchor state — missing DLT requirement #6 contract-readable state, §9.3/§7.4: Permissionless anchoring enables thread pollution and dispute-freeze griefing #13 party bindings).
• Bonds OPTIONAL (no arbiter fee to fund; symbolic spam-friction bond allowed).
• Honest scoping: deterrence is reputational — anchored assert/dispute/enforce history feeds §5.4 reputation, so systematic formula-capture prices itself out. Fit for repeat-player ecosystems; against one-shot/adversarial counterparties, use the optimistic profile, prepayment, or no escrow. This honesty is stated in the profile text and the new §11 row.

§9.2 restructured so each process_profile declares its own required clause fields (the optimistic MUSTs don't apply to a profile with no arbiter).

Closes #21

Affected spec section(s)

§6.2.1 (fourth enforcement path), §9.2, §9.4 (profile definition), §10.3, §11, §14, Appendix A, Appendix C.

Trust impact

Per-Thread opt-in trade, made explicit: Threads selecting the small-claims profile drop the arbiter/panel trust root entirely (no forum) and instead rest on (a) the pre-agreed formula enforced by the escrow contract — the existing chain root — and (b) reputational incentives, which the profile text names as the deterrent rather than implying monetary enforcement. Threads on the default optimistic profile are unaffected.

Checklist

• One logical change, conventional PR title
• Cited the affected spec section(s)
• Stated the trust impact (or "none")
• Normative language uses RFC 2119 keywords correctly
• docs-check passes