fix(dsh-plugin-browserskill): address review findings (leaks, trust fence, queue race)

Blocking:
- B1: delete screenshot scratch PNGs — observation frames reuse one fixed
  per-session path and unlink after every read (finally); browser_screenshot
  unlinks once the bytes are in the attachment store (kept only when the file
  itself is the model-facing artifact).
- B2: replicate dsh's browser-trust fence on /bsk-observation/*: loopback
  Host only, Origin must match Host, sec-fetch-site: cross-site refused, POST
  requires application/json; README documents the loopback trust premise and
  the 0.0.0.0 warning.

Major:
- M1: KeyedExecutor tail chains previous+task (allSettled) so a task aborted
  while queued cannot release the next one into the running session.
- M2: client tracks the live frame per session — replacing/removing/reset
  revokes the old blob URL at once; loads settling after replacement never
  resurrect it.

Minor: drop replaced thumbRefs (+on remove); beginAction fires inside the
queue (no label overwrite while queued, no idle flash); half-initialized
session cleanup stops through the queue with one retry; SSE (re)open refetches
/state (+ snapshot flag renamed subscribed); install probe uses --version (no
daemon spawn); emulate mobile documents the width+height requirement (the
daemon refuses it alone — verified).

Nit: single BskRunOptions declaration; tails map entry dropped on drain; SSE
cleanup on res close; popOut catches requestWindow rejections; resize handle
gains keyboard control (arrows, 16px steps, aria value attrs).

Tests: +14 (fence rules, scratch lifecycle, queue race, blob revocation,
instrumentation timing, SSE resync). 113/113 green.

packages/dsh-plugin-browserskill/src/runner.ts

@@ -48,18 +48,13 @@ export interface BskRunResult {
 export interface BskRunOptions {
   signal?: AbortSignal;
   timeoutMs?: number;
+  /** Opaque routing tag (e.g. a session id) enabling per-tag kills. */
+  tag?: string;
 }
 
 /** Minimal spawn signature so tests can substitute a fake child process. */
 export type SpawnImpl = (command: string, args: string[]) => ChildProcess;
 
-export interface BskRunOptions {
-  signal?: AbortSignal;
-  timeoutMs?: number;
-  /** Opaque routing tag (e.g. a session id) enabling per-tag kills. */
-  tag?: string;
-}
-
 export interface BskRunner {
   /** Run `bsk <args...> --json` and collect its output. */
   run(args: string[], options?: BskRunOptions): Promise<BskRunResult>;