Log and reject unknown `messageType` values in `receiveMessage`

[arasaka-net]

receiveMessage in src/scripts/p2p.js silently drops any message whose messageType does not match an enumerated case. Add a default branch that logs the offending payload and cover it with a test.

Context
The P2P layer is the trust boundary between the wire and the local board. When a peer sends a message with an unrecognized messageType — because of a version skew, a bug, or a malformed payload — receiveMessage currently falls through the outer switch with no warning, no log, and no banner. The receiving client has no way to know a message was ignored, which produces exactly the kind of silent desync the table should make visible. A bounded fix is to add a default: branch that logs the full message via console.warn and returns, mirroring the existing warnings on missing elements for grab-element, move-element, and ungrab-element. A matching unit test locks the behavior in.

Affected Files

• src/scripts/p2p.js:124 — Add a default: branch to the outer switch (message.messageType) that logs the full message via console.warn and returns without mutating the DOM.
• src/scripts/p2p.js:80 — Add a default: branch to the inner switch (message.entityType) inside create-element for the same reason.
• src/scripts/p2p.test.js — Add tests that assert unknown messageType and unknown entityType values log a warning and do not touch the DOM.

Requirements

• receiveMessage logs a warning when it receives a message with an unknown messageType.
• receiveMessage logs a warning when a create-element message carries an unknown entityType.
• Neither case mutates the DOM or dispatches any CustomEvent.
• A Vitest test spies on console.warn and verifies both behaviors.
• npm test and npm run lint pass after the change.

Verification

• npm test -- src/scripts/p2p.test.js
• npm run lint
• grep -n 'default:' src/scripts/p2p.js

Not In Scope

• Do not introduce a message schema validator or type guards beyond the default: branches.
• Do not add a protocol version field — that is a separate change.
• Do not refactor the outer switch into a dispatch table.

Evidence

• src/scripts/p2p.js:48-124 — Outer switch (message.messageType) has no default: branch; unknown types fall through silently.
• src/scripts/p2p.js:50-80 — Inner switch (message.entityType) inside create-element has no default: branch; unknown entities are silently ignored.
• src/scripts/p2p.js:86 — grab-element already logs receiveMessage: grab-element ignored — no element with id ... — the same warning style should apply to the new default branches.

_{Arasaka Queue Planning Division.}