fix(server): forward authInfo/agent/toolName ctx to AccountStore.upsert and list (#1310)

[bokelley]

Closes #1310

AccountStore.upsert and AccountStore.list captured _ctx in the framework dispatcher but discarded it, silently blocking any adopter who needs the calling principal (e.g. for the per-agent billing gate BILLING_NOT_PERMITTED_FOR_AGENT from adcp#3831). This PR adds optional ctx?: ResolveContext to both interface methods (non-breaking — existing implementations compile unchanged) and updates buildAccountHandlers to forward authInfo, agent, and toolName using the same pattern already established for accounts.resolve at lines 1009-1012. Also fixes the identical pre-existing ctx.agent omission in the reportUsage and getAccountFinancials dispatcher blocks in the same function.

What was tested

• npm run format:check — passed
• npx tsc --project tsconfig.lib.json — only pre-existing TS2688/TS5107 tsconfig warnings (not code errors); no new errors introduced
• test/server-decisioning-from-platform.test.js — 109/109 pass (2 new ctx-forwarding tests added for upsert and list)
• Full suite (test/*.test.js test/lib/*.test.js) — 232 failures before and after; no new failures

Pre-PR review

• code-reviewer: approved — no blockers; noted #3851→#3831 reference (fixed in follow-up commit) and missing ctx.agent test coverage as issues (no blocker); as const removal is intentional cleanup
• ad-tech-protocol-expert: approved — non-breaking per spec; ResolveContext is correct shape for upsert/list; sync_accounts/list_accounts toolName strings are correct wire names; Phase 2 caveat added to JSDoc per reviewer recommendation

Nits (not fixed, surfaced for human reviewer)

• ctx.agent forwarding is untested — wiring a full BuyerAgentRegistry in a test is medium complexity; the authInfo+toolName tests cover the new dispatcher path and the ctx.agent branch follows identical conditional-spread logic. A follow-up can add registry-backed agent forwarding tests once Phase 2 (feat(server): BuyerAgentRegistry Phase 2 — wire billing-capability enforcement (AdCP 3.1) #1292) lands.
• The #3851 reference in the original issue (vs adcp#3831 used throughout the codebase for BILLING_NOT_PERMITTED_FOR_AGENT) may indicate a distinct follow-up spec PR — if so, the JSDoc reference should be revisited when that PR merges.

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[bokelley]

Superseded — the same fix landed in #1315 (forwards ctx to AccountStore.upsert/list, closing #1310) and was further generalized in #1321 (the symmetric toResolveCtx helper covering all account-store call sites). Issue #1310 is closed. Thanks for the work — closing as duplicate.