fix(plugins): the silent-degrade doors close — a broken accelerator install can never read as absent

The auto-detection "not installed" heuristic accepted any resolution failure
whose message merely CONTAINED the package name, unterminated — so a missing
platform-binary sibling package (what a deploy replacing node_modules
mid-restart leaves behind) read as "the accelerator is not installed", and
brainy silently served the default WASM engines with zero journal lines. A
production restart storm paid 90 seconds of throttled WASM compile behind
exactly that hole. The name must now terminate where it ends (quote,
whitespace, punctuation, end) — a sibling package, an inner file path, or a
dependency failure is a broken install and init() throws, as the guard's own
law always stated.

Second door: activate() returning false (the documented graceful decline)
warned on console.warn, which `silent: true` patches away — an invisible
degrade. The decline now narrates via the always-on channel.

Also exports CanonicalCounts from the public surface (the coverage-ledger
denominator type consumers read through getCanonicalCounts()).

Pinned in tests/unit/plugin-activation-loudness.test.ts (five error shapes;
the decline warn under silent: true).

src/plugin.ts

@@ -9,6 +9,7 @@
  * registered manually via `brain.use()` — there is no implicit detection.
  */
 
+import { prodLog } from './utils/logger.js'
 import type {
   StorageAdapter,
   Vector,
@@ -1574,9 +1575,13 @@ export class PluginRegistry {
         this.activated.add(name)
         activated.push(name)
       } else {
-        // Documented graceful decline (activate() → false). Surface it loudly so
-        // a silent degrade to the default engine never goes unnoticed.
-        console.warn(
+        // Documented graceful decline (activate() → false). Surface it on the
+        // ALWAYS-ON channel: `silent: true` patches console, and a declined
+        // accelerator warned into a patched console is a silent degrade to the
+        // default engines — the exact invisible-fallback class this registry
+        // exists to prevent (a production storm ran the WASM engine for 90s
+        // behind one suppressed warn).
+        prodLog.warn(
           `[brainy] Plugin "${name}" declined activation (activate() returned false); ` +
             `the default engine is in use for its providers.`
         )