feat: add nearby agent messaging

[christopherjnelson]

Implementation

• Adds message as a first-class, exclusive agent turn action across shared contracts, the deterministic world engine, both providers, the API, World Lab, telemetry, and exports.
• Delivers typed accepted-message events and bounded recent communication observations.
• Adds chronological inbound/outbound communication entries to the event log and selected-agent inspector.

Messaging rules

• The authoritative server trims content and requires 1–280 plain-text characters.
• A recipient must exist, cannot be the sender, and must be within inclusive H3 grid distance three at the beginning of the turn; co-located agents are eligible.
• Accepted messaging consumes the entire turn. Rejected actions deliver no message and produce no accepted event.
• Recent observation context is chronological and capped at six inbound/outbound messages. Replies are optional and never automatic.

Architecture and security

• The deterministic world engine remains the sole authority for recipient and range validation and world mutation.
• Agent-authored message text is bounded, treated as untrusted subordinate content, and rendered as React text rather than HTML.
• Fixed instructions explicitly preserve game-rule and prompt authority over received claims or instructions.
• No raw prompts, provider responses, private reasoning, credentials, authorization data, or unbounded diagnostics are exposed.
• Communication memory is derived from accepted world events; reset clears it, and process restart remains non-persistent.

Telemetry and schema v2

• Experiment exports now require schemaVersion: 2, reflecting the message action, communication records, messaging metrics, and communication-aware agent filtering.
• Adds requested/delivered message and sent/received communication metrics.
• A communication is relevant to both sender and recipient, while a turn remains owned by its acting agent. Agent-scoped exports include that agent's accepted inbound and outbound messages and exclude unrelated communications.
• Rejected message attempts remain visible only through relevant rejected sender turns and are never represented as delivered communications.
• Canonical communication records remain separate from non-communication world events; initial and current world snapshots remain state-only.
• Agentborne does not ingest exports, so this change intentionally adds no v1 migration or compatibility layer.

Automated testing

• Adds deterministic shared-contract, engine/service, provider/runtime, telemetry/export, API, React, and Playwright coverage for messaging, rejection, bounded context, escaping, filtering, reset, and schema v2.
• Final local gate passed: formatting, lint, type checking, 146 unit/integration tests, the production build, and the deterministic Playwright flow.
• Chromium installation was checked with pnpm exec playwright install chromium; no live-provider smoke test was run.

Genuine-provider manual validation

• A previously completed opt-in experiment produced 81 accepted turns: 56 moves, 23 infections, and two accepted Mingle-to-Ember messages, both at distance zero.
• Mingle retained its earlier outbound context, and Ember received both messages in subsequent observations.
• The run had no provider errors, rejected turns, or unsafe export fields.
• An Ember-only, message-only export contained zero Ember-owned message turns, both inbound communications, and no unrelated communication records.
• Downloaded exports and screenshots are intentionally not included in this PR.

Deferred functionality

• Relationships, reputation, alliances, factions, teams, shared missions, persistent or semantic memory, group chat, broadcasts, player messaging, notifications, automatic replies, persistence/databases, provider configuration UI, and map communication animations remain out of scope.