fix(wasm): bind dynCall_* to real DYNCALLS=1 exports; refactor shim into files

The shim bound bare dynCall_* names to JS getWasmTableEntry() calls, bypassing
the asyncify-instrumented dynCall_* wasm trampolines that -sDYNCALLS=1 provides.
That broke Asyncify unwind/rewind through indirect calls -> "indirect call
signature mismatch" (caught every frame in Firefox; fatal renderer crash in
Chrome). Bind the bare names to wasmExports["dynCall_<sig>"] instead.

Result: the PCBnew "select draw lines" e2e is green in Firefox (tool selects and
draws, zero page errors). Dropped the fiber-stabilization block, the shipped
diagnostic block, and the exportCallStack JS hack (all compensated for the wrong
binding); shim shrank 521 -> ~250 lines.

- scripts/common/inject-dyncall-shims.sh: orchestrator only; injected JS extracted
  to scripts/common/shims/
- scripts/common/shims/dyncall-binding.js.tmpl: per-signature binding template
- scripts/common/shims/handlesleep.js: nested-Asyncify handleSleep fix (#9153)
- scripts/common/shims/diagnostics.js: logging-only, opt-in via SHIM_DIAGNOSTICS=1
- tests/package.json: add test:kicad:firefox / test:kicad:chrome scripts

Known issue (tracked separately): Chrome still renderer-crashes on the first
coroutine resume. Asyncify.doRewind replays the deep main-context call stack and
exceeds V8's execution-stack limit (Firefox tolerates the same wasm). Proper fix
is JSPI.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/package.json

@@ -9,8 +9,10 @@
     "build-wasm": "cd apps && make -f Makefile.wasm",
     "serve": "npx serve apps -p 8080 -c ../serve.json",
     "setup:kicad": "./scripts/setup-kicad-wasm.sh",
-    "test:kicad": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=firefox --headed",
-    "test:kicad:headed": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=chromium --headed"
+    "test:kicad:firefox": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=firefox",
+    "test:kicad:chrome": "npm run setup:kicad && playwright test --config=playwright-kicad.config.ts --project=chromium --headed",
+    "test:kicad": "npm run test:kicad:firefox",
+    "test:kicad:headed": "npm run test:kicad:chrome"
   },
   "devDependencies": {
     "@playwright/test": "^1.40.0",