HS: cookie API (+3 tests, partial)

Three-part change: (a) tests/hs-run-filtered.js gets a per-test
__hsCookieStore Map, a globalThis.cookies Proxy, and a
document.cookie getter/setter that reads/writes the store. Per-test
reset clears the store. (b) generate-sx-tests.py declares cookies in
the test header and emits hand-rolled deftests for basic set / update
/ length-when-empty (the three tractable tests). (c) regenerated
spec/tests/test-hyperscript-behavioral.sx via mcp_hs_test.regen.

No .sx edits — `set cookies.foo to 'bar'` already compiles to
(dom-set-prop cookies "foo" "bar") which routes through host-set!.

Suite hs-upstream-expressions/cookies: 0/5 → 3/5.
Smoke 0-195 unchanged at 170/195.

Remaining `basic clear` (needs hs-method-call host-call dispatch) and
`iterate` (needs hs-for-each host-array recognition) need runtime.sx
edits — deferred to a future sx-tree worktree.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plans/hs-conformance-scoreboard.md

@@ -4,10 +4,10 @@ Live tally for `plans/hs-conformance-to-100.md`. Update after every cluster comm
 
 ```
 Baseline:   1213/1496 (81.1%)
-Merged:     1277/1496 (85.4%)   delta +64
+Merged:     1280/1496 (85.6%)   delta +67
 Worktree:   all landed
 Target:     1496/1496 (100.0%)
-Remaining:  ~219 tests (clusters 17/22/29/31/32 blocked; 31/32 need dedicated sx-tree worktree)
+Remaining:  ~216 tests (clusters 17/22/29/31/32 blocked; 31/32 need dedicated sx-tree worktree; 33 partial)
 ```
 
 ## Cluster ledger
@@ -63,7 +63,7 @@ Remaining:  ~219 tests (clusters 17/22/29/31/32 blocked; 31/32 need dedicated sx
 |---|---------|--------|---|
 | 31 | runtime null-safety error reporting | blocked | — |
 | 32 | MutationObserver mock + `on mutation` | blocked | — |
-| 33 | cookie API | pending | (+5 est) |
+| 33 | cookie API | partial | +3 |
 | 34 | event modifier DSL | pending | (+6–8 est) |
 | 35 | namespaced `def` | pending | (+3 est) |
 
@@ -88,7 +88,7 @@ Defer until A–D drain. Estimated ~25 recoverable tests.
 | A      | 12   | 4       | 0       | 0       | 1       | —           | 17    |
 | B      | 6    | 0       | 0       | 0       | 1       | —           | 7     |
 | C      | 4    | 0       | 0       | 0       | 1       | —           | 5     |
-| D      | 0    | 0       | 0       | 3       | 2       | —           | 5     |
+| D      | 0    | 1       | 0       | 2       | 2       | —           | 5     |
 | E      | 0    | 0       | 0       | 0       | 0       | 5           | 5     |
 | F      | —    | —       | —       | ~10     | —       | —           | ~10   |