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

lib/versioned-map.ts

@@ -183,4 +183,12 @@ export default class VersionedMap<K, V> {
         this.map.delete(k);
     }
   }
+
+  public *[Symbol.iterator](): IterableIterator<[K, V]> {
+    for (const [key, revisions] of this.map) {
+      const last = revisions[revisions.length - 1];
+      if (last === NONEXISTENT) continue;
+      yield [key, last as V];
+    }
+  }
 }