docs: signer is in-tree - align custody claims after #7/#8 merged

#7 (signer) and #8 (builder hardening) merged into main this morning; this
branch is rebased onto the result and packages/signer is now in-tree. Three
sites still said pairing the signer with the hosted builder "does not yet
remove the custody exposure" (true when #7 was written, before this PR's
keyless build_* tools existed - now false for the wallet/tx/contract family):

- README.md's "Local signer" section: now states the 4-call non-custodial
  flow (signer_get_address -> build_* -> signer_sign -> submit -> await) is
  live today for that family, names the signer's four tools, and keeps the
  agent-registry/self-improvement families explicitly scoped out.
- packages/signer/README.md's "Known limitations" bullet and "Running it"
  closing line: same correction, with the specific now-keyless build_* tool
  names and an accurate (not overclaiming) description of what the E2E test
  exercises - it signs with the same CML primitives sign.ts uses, as a
  stand-in for calling vector_signer_sign directly, not a call into the
  signer package's own code.

Grepped case-insensitively across the repo for "does not yet remove" /
"custody exposure" / "signer half is ready" / "builder half is not yet"
before and after: exactly these 3 sites found, all corrected, zero stale
instances remain.

packages/signer/README.md

@@ -144,17 +144,28 @@ over-counts, which refuses too much rather than too little.
 - **Prompt injection is bounded, not eliminated.** Policy refuses out-of-limit
   transactions, but an injected agent can still cause any transaction *within* policy.
   Recipient allowlisting is the next lever.
-- **Pairing this signer with the hosted builder does not yet remove the custody exposure it
-  is designed to fix.** The signer's own four tools are complete and independently verified
-  end to end against live chain data (`test/integration/roundtrip.test.ts`). What is not yet
-  true is a wired-up keyless round trip through the hosted *builder's* actual tools: today
-  every builder tool that builds or sends a transaction (`vector_send_apex`,
-  `vector_build_transaction`, the registry and governance tools, ...) still requires your
-  mnemonic as a call parameter, and no `submit_transaction` tool exists yet to submit a
-  transaction this signer produced. That migration is tracked separately in
+- **Pairing this signer with the hosted builder now removes the custody exposure it was
+  designed to fix — for the wallet, transaction, and smart-contract family.** The signer's own
+  four tools are complete and independently verified end to end against live chain data
+  (`test/integration/roundtrip.test.ts`), and the hosted *builder's* tools in that family are
+  keyless: `vector_build_send_apex`, `vector_build_send_tokens`, `vector_build_transaction`,
+  `vector_build_deploy_contract`, and `vector_build_interact_contract` all take a wallet
+  *address*, never a mnemonic, and `vector_submit_transaction` / `vector_await_transaction`
+  complete the round trip. The pipeline — hosted keyless build → sign → submit → await — is
+  E2E-proven on Vector testnet (`packages/builder/test/integration/keyless-e2e.test.ts`): a
+  builder-produced unsigned transaction is signed with the same CML primitives `sign.ts` uses
+  (hash the body, produce a vkey witness, attach it — explicitly a stand-in for calling
+  `vector_signer_sign` directly, not a call to this package's own code), then submitted and
+  confirmed on real Vector testnet blocks. This signer's own tool surface, policy engine, and
+  audit log are exercised separately, by this package's own suite
+  (`test/integration/roundtrip.test.ts` and the smoke tests above). **What is still open: the
+  agent-registry and self-improvement tool families.** Their tools still require your mnemonic
+  as a call
+  parameter, so pairing this signer with the builder does not yet cover them. That migration is
+  tracked separately in
   [`docs/architecture/non-custodial-split.md`](../../docs/architecture/non-custodial-split.md)
-  (PRs 6-8) and has not shipped. Until it does, the root README's custody notice still
-  describes the hosted builder accurately.
+  and has not shipped. Until it does, the root README's custody notice still describes those two
+  families accurately.
 
 ## Running it
 
@@ -180,9 +191,10 @@ example):
 }
 ```
 
-Register it alongside the hosted builder so an agent has both sets of tools available. See the
-last bullet under Known limitations above before expecting that pairing to keep your mnemonic
-off the hosted server today — the signer half is ready; the builder half is not yet.
+Register it alongside the hosted builder so an agent has both sets of tools available. For the
+wallet, transaction, and smart-contract family, this pairing keeps your mnemonic off the hosted
+server today — both halves are ready. See the last bullet under Known limitations above for
+what's still open: the agent-registry and self-improvement families.
 
 ## Testing