harden: stop the background reading the shared state singleton, and enforce it at build time (closes #324)

Five defects, one of which destroyed every wallet, came from src/background reading and writing the module-level state singleton the MV3 worker never populates, which silently served DEFAULT_STATE. Each point fix created the next defect. The background now has its own per-call getState() and a queued read-modify-write updateState(); the singleton is unreachable from it, and an unpopulated read throws instead of serving defaults.

The prohibition is enforced by the build, not by review: build.js asserts over esbuild's own metafile that no forbidden module is an input of a background bundle, so every specifier syntax esbuild resolves is covered, and both halves of the table are checked for rot -- a stale key, a stale module, an empty list, or an unlisted entry point under src/background/ all fail the build. The ESLint rule remains as fast local feedback and reads the same shared table. Known bounds are documented where the table lives.

Also closes #320: getProvider() now requires a validated network id, so a cold worker no longer prepares a non-mainnet dApp transaction for mainnet and gets refused by the wallet's own verifier. backgroundRefresh() no longer mutates address objects across a network round trip, the broadcast path takes its endpoint and chain id from one snapshot, and eight test storage stubs now structured-clone on get as the real chrome.storage.local does.

closes #320

tests/deleteAddress.test.js

@@ -19,6 +19,14 @@ const {
     balanceWarningHtml,
 } = require("../src/popup/views/deleteAddress");
 const { prices, clearPrices } = require("../src/shared/prices");
+const { state } = require("../src/shared/state");
+
+// The screen prices holdings, and pricing asks which chain it is on. Reading
+// the singleton's network before anything loaded it now throws rather than
+// answering mainnet by default
+// (https://git.eeqj.de/sneak/AutistMask/issues/324), so the network this
+// fixture is on is stated instead of assumed.
+state.networkId = "mainnet";
 
 const USDC = "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48";