feat: add bounded admin WebSocket backend (Phase 8D.5)

- Require current admin cookie sessions, Origin checks and single-use
  tickets
- Reuse the shared console with session-aware authorization and slot
  allocation
- Add HTTPD-owned I/O, bounded buffering and revocation cleanup
- Prevent LRU eviction of serial clients and stale admin socket closure
- Reject unsupported web-shell mutations before side effects
- Add host regressions, a smoke client and resource accounting

Validated by user sign-off after a 15-minute full-client soak at 230400
baud, with a few broker drops under heavy output. Browser UI remains
for Phase 8D.6; numeric memory reserves remain open.

tests/admin_console_boundary/run.py

@@ -4,10 +4,13 @@
 No target scheduler, socket library, or hardware execution is claimed.
 """
 from pathlib import Path
+import os
 import subprocess
 import tempfile
 
 ROOT = Path(__file__).resolve().parents[2]
+IDF = Path(os.environ.get("IDF_PATH", str(Path.home() / ".platformio/packages/framework-espidf")))
+parser = str(IDF / "components/console/split_argv.c")
 source = (ROOT / "src/admin_ssh_console.c").read_text()
 header = (ROOT / "src/admin_ssh_console.h").read_text()
 def strip_includes(text):
@@ -21,18 +24,18 @@ with tempfile.TemporaryDirectory(prefix="admin-console-boundary-") as directory:
             + (ROOT / "tests/admin_console_boundary/test.c").read_text())
     (path / "test.c").write_text(unit)
     subprocess.run(["cc", "-std=c11", "-Wall", "-Wextra", "-Werror",
-                    "-g", str(path / "test.c"),
+                    "-g", str(path / "test.c"), parser,
                     "-o", str(path / "test")], check=True, timeout=30)
     subprocess.run([str(path / "test")], check=True, timeout=10)
     ssh = (ROOT / "src/ssh_transport.c").read_text()
-    adapter = ssh[ssh.index("static bool admin_console_drained("):
-                  ssh.index("static bool consume_external_close(")]
+    adapter = ssh[ssh.index("static admin_ssh_console_token_t admin_console_token("):
+                  ssh.index("static void *ssh_malloc(")]
     unit = ((ROOT / "tests/admin_console_boundary/fakes.h").read_text()
             + strip_includes(header) + "\n" + strip_includes(source)
             + (ROOT / "tests/admin_console_boundary/adapter.c").read_text()
             + adapter + "\nint main(void) { test_adapter(); }\n")
     (path / "adapter.c").write_text(unit)
     subprocess.run(["cc", "-std=c11", "-Wall", "-Wextra", "-Werror",
-                    "-Wno-unused-variable", str(path / "adapter.c"),
+                    "-Wno-unused-variable", str(path / "adapter.c"), parser,
                     "-o", str(path / "adapter")], check=True, timeout=30)
     subprocess.run([str(path / "adapter")], check=True, timeout=10)