HS: implicit variable declaration, console mock, increment/decrement fix

Integration:
- hs-collect-vars: scan compiled SX for set! targets, collect symbols
- hs-handler: pre-declare collected variables in closure let-bindings
  so increment/decrement work on first use (variable persists across
  event handler calls via closure scope)

Compiler:
- Fix emit-inc/emit-dec: use expr (variable) not tgt-override (element)
- Simplify to plain (set! x (+ x amount)) since vars are pre-declared

Mock DOM:
- Add mock console object to host-global
- Add console handler (no-op) to host-call dispatch
- Override console-log/debug/error as no-op primitives to avoid
  str hitting circular refs in mock DOM elements

Fixes 4 log timeouts, 2+ increment/decrement failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/hyperscript/compiler.sx

@@ -364,10 +364,7 @@
           (true
             (let
               ((t (hs-to-sx expr)))
-              (list
-                (quote set!)
-                t
-                (list (quote +) (list (quote or) t 0) amount)))))))
+              (list (quote set!) t (list (quote +) t amount)))))))
     (define
       emit-dec
       (fn
@@ -416,10 +413,7 @@
           (true
             (let
               ((t (hs-to-sx expr)))
-              (list
-                (quote set!)
-                t
-                (list (quote -) (list (quote or) t 0) amount)))))))
+              (list (quote set!) t (list (quote -) t amount)))))))
     (define
       emit-behavior
       (fn