feat: add Parallel Emission opt-in across protocol surfaces

[spacexun2]

Summary

This implements Slice 1 — Parallel Emission of the split described in #62 (refs #62). Slice 2 (per-task probes, Next Probe At, Silent Kick / Captain Wake / Mailbox Wake) follows separately; nothing in that slice is touched here.

Parallel Emission is the opt-in ability for models that can emit several agent_teams_* tool calls in one assistant message. It is a single boolean in the new agent-teams settings namespace, parallelToolCalls, default off, surfaced as a 支持工具并行 checkbox on the plugin's Plugins-configuration card:

• Host: when the settings service exists, the plugin lazily registers the agent-teams namespace with exactly one field (schema default false). Without the service (headless profiles, older hosts) the registration never happens, the switch reads false, and everything else is unaffected.
• Protocol surfaces branch on the live value: the captain usage section is evaluated at assemble time, member personas freeze the value at spawn (already-spawned members are never rewritten), and assignment prompts read it at dispatch. When on, the surfaces allow claim + in_progress, completed + report, and several create_task calls in one response; when off, the surfaces keep the serial protocol — member personas and assignment prompts are byte-identical to the previous text, and the usage section adds one explicit serial sentence ("Issue one agent_teams_* tool call per response ..."). Same-response calls still execute in order, so later creates can reference earlier ids from the same response — and dependency ids must still exist: create_task rejects unknown dependencies exactly as before (pinned by a new lifecycle check; PR 通过消除 status 轮询和启用并行工具调用减少 token 浪费 #48's empty-dependency branch stays rejected).
• Web client: a Plugins-tab card keyed by the agent-teams namespace under the settings.plugin.item type-only slot contract. Both client imports are type-only and all writes go through the cordis settingsScope service, so the bundle purity gate mechanically guarantees no cross-plugin value import. The checkbox is disabled when the namespace is not served or the settings document is read-only (memory mode). It never writes maxParallelToolCalls — the Agent Loop execution pool stays on the Agent Loop card (negative source pins enforce this).

Docs: one sentence in each README's Configuration section and a short section in docs/usage.md.

Validation

• tsc -p tsconfig.json --noEmit, tsc -p tsconfig.client.json --noEmit, and the full build (clean-build + both tsc passes + tsdown, including the client bundle purity gate) pass.
• node scripts/verify.mjs: all 184 checks pass, including new pins for the settings schema default ({} resolves parallelToolCalls: false), persona / assignment / usage on-vs-off branches, the type-only Plugins-tab registration keyed by the namespace, and negative guards keeping maxParallelToolCalls out of this plugin's sources.
• node scripts/lifecycle-verify.mjs drives the real compiled create_task with a never-created dependency id and asserts it fails loud (no forward references).
• fallback-tdd, member-failure-tdd (both harness modes), quality-gates-tdd, harness-compat-tdd, web-routes-verify, release-metadata, http-body, compatibility, doctor, and stress-verify all pass; node --test scripts/compatibility.test.mjs additionally skips its doctor-bin-symlink case on this machine (EPERM: operation not permitted, symlink — Windows without symlink privilege), reproduced identically on clean main.
• Known-local flake note: two lifecycle-verify checks (unfinished captain takeover returns to a member when the captain becomes idle, activity refines residency through the live Agent registry) fail intermittently on this machine on clean main as well (reproduced in a pristine worktree, plain and --modern-harness variants) — pre-existing timing flakiness, unrelated to this branch.

Slice 2 follow-up will cover the per-task probe clock and the protocol rewrites around polling, wake, and end-of-turn.