refactor: replace array-based expressions with typed class hierarchy

Replace the old Lisp-like array expression representation
(["AND", ["PARAM", ...], ...]) with a class hierarchy rooted in
an abstract Expression class (Literal, Parameter, Binary, Unary,
FunctionCall, Conditional). This gives compile-time type safety
to expression construction, evaluation, and pattern matching.

Key changes:
- New lib/common/expression.ts defines the class hierarchy with
  map/evaluate/toString methods
- Rewrite parser as hand-rolled recursive descent, removing the
  parsimmon dependency
- Extend Path with a colon separator to unify parameter identity
  and attributes into a single address space (e.g.
  "Device.WiFi.SSID.1.Name:writable"). The colon field tracks
  how many trailing segments are attribute qualifiers. PathSet
  rewritten with separate param/attr segment indexes
- Flatten device attribute representation in the UI to
  colon-delimited keys mirroring the new path syntax

ui/drawer-component.ts

@@ -18,6 +18,7 @@ import {
   queueTask,
   StageTask,
 } from "./task-queue.ts";
+import Expression from "../lib/common/expression.ts";
 
 const invalid: WeakSet<StageTask> = new WeakSet();
 
@@ -95,7 +96,7 @@ function renderStagingSpv(task: StageTask, queueFunc, cancelFunc): Children {
 function renderStagingDownload(task: StageTask): Children {
   if (!task.fileName || !task.fileType) invalid.add(task);
   else invalid.delete(task);
-  const files = store.fetch("files", true);
+  const files = store.fetch("files", new Expression.Literal(true));
   let oui = "";
   let productClass = "";
   for (const d of task.devices) {