chore(preflight): bump skill integrity pin for v3 (address-book invariant)

[szhygulin]

Coordinated with `vaultpilot-skill#4` — same shape as the previous v1→v2 pin coordination for NEAR Intents.

Summary

The `vaultpilot-preflight` skill picks up Invariant #7 in v3 — agent-side rules for the address-book v1.0 surface that ships in #284:

• Verification-block recipient suffix → agent behavior table ((contact: Mom — verified) vs ⚠ contacts file failed verification etc.)
• Lead-with-warning rule for the contacts-tamper marker
• Sign-message-during-prepare-flow anomaly rule (now that `personal_sign` is in the WC namespace)
• Post-`add_contact` cross-check via `verify_contacts`

That content change shifts both the SHA-256 of `SKILL.md` and the in-file integrity sentinel (`v2_43b1d2403a0c2a94` → `v3_2d3b876b38550fe5`).

This MCP pins both values in source (`src/index.ts` ~lines 1270 + 1275-1276). The pin must be bumped to the new values, otherwise every `prepare_` / `preview_` flow will fail the integrity check.

Why three coordinated changes (#284 + skill#4 + this)

• `feat(contacts): address book v1.0 — BTC + EVM #284` adds the address-book feature.
• `vaultpilot-skill#4` documents the agent-side invariant for it.
• This PR aligns the MCP's pinned hash with the new skill content.

Merge order doesn't strictly matter (the only known user is the author), but the cleanest sequence is: skill PR → this PR → #284. The intermediate state where #284 is unmerged but the pin is bumped is benign — agents call `add_contact` and get `unknown tool`; the integrity check itself runs fine against the new SKILL.md.

Test plan

• `npm run build` clean
• `grep` confirms no leftover `v2` / old-SHA references
• New SHA matches `sha256sum` output of the new `SKILL.md`
• After all three PRs merge: trigger any `prepare_*` flow in a fresh session — the integrity check should pass with the new pin

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