docs: agent-registry family is keyless - tool tables, custody scope, spend-limit copy

README, .env.example, packages/signer/README.md, and docs/architecture/non-custodial-split.md
updated for the family-2 keyless migration (agent-registry build_* tools, no mnemonic
parameters): security notice narrowed to name the Self-Improvement Module as the only
remaining custodial family; agent-registry tool table renamed to the five build_* rows;
features bullets, self-hosting copy, Configuration/spend-limit scope notes, and the
architecture diagram's Safety Layer footnote all updated to "self-improvement only"; signer
README's pairing-status bullet and closing line extended to cover wallet/tx/contract AND
agent-registry; architecture doc's PR-sequence table marks family 2 as landed.

docs/VECTOR.md gains five new tool sections (register/update/transfer/deregister/message) -
this doc never documented the registry family under any name before, so these are additions
rather than renames; keyless framing (changeAddress, no mnemonic, unsigned CBOR + 4-call flow)
matches the style of the existing wallet/tx/contract sections. Safety Controls section's
custodial-family list also corrected to self-improvement only.

docs/architecture/non-custodial-split.md

@@ -189,7 +189,7 @@ TDD throughout: failing test before implementation, every PR.
 | **4** | **Signer package** (purely additive): `KeySource`, decode, `PolicyEngine`, audit, 4 tools. Heavy TDD | no |
 | **5** | Builder hardening: auth (enforced when configured), per-identity rate limits, `submit_transaction`, `await_transaction` | no |
 | **6** | **Family 1 — wallet/tx keyless.** Mnemonics removed; `build_*` tools land ✅ **(landed — this PR)** | **yes** |
-| **7** | **Family 2 — agent registry keyless.** Drops `@ts-nocheck` from `agent-network.ts` | yes |
+| **7** | **Family 2 — agent registry keyless.** Drops `@ts-nocheck` from `agent-network.ts` ✅ **(landed — this PR)** | yes |
 | **8** | **Family 3 — governance keyless.** Plus env-driven ref-UTxO config and a CBOR encoding fix | yes |
 | **9** | Mainnet cutover: README, security-page correction, deliberate `workflow_dispatch` | — |