feat(dsh-plugin-browserskill): reveal tool schemas only after skill invocation

Progressive disclosure, final stage: with lazyTools on (default), the eleven
browser_* tool schemas stay out of the system prompt — the browser-skill
catalog entry is the sole advertisement. One successful skill invocation
(model tool call via tools/result, or a /browser-skill user gesture via the
session append feed) registers the suite for the process lifetime, idempotent
on repeats; session resume is covered by scanning durable events for a past
tool/call+tool/result pair (or skill-invocation message) on session entry and
at apply time. lazyTools: false keeps the legacy always-on registration.

Investigation (recorded in the ticket): tools/result carries normalized
name/arguments with an isError discriminant; dsh 0.1 has no official global
visibility switch (ctx.tools.restrict is agent-scoped and throws from a plain
context), making conditional registration the intended pattern; per-step
assembly picks the new suite up on the next step, and visibility changes are
first-class inputs of tool-skill's catalog digest. registerTools now returns
the combined disposer via a prototype-preserving tracking overlay; the skill
prelude tells the model the browser_* tools unlock on skill load.

Tests: +8 (hidden-before/reveal/idempotent/gesture/history hit+miss/dispose/
scanner pairing/two-state apply wiring). 124/124 green.

packages/dsh-plugin-browserskill/skill/prelude.md

@@ -5,6 +5,11 @@ through this plugin's `browser_*` tools. Each tool spawns `bsk <cmd> --json` —
 same engine the canonical CLI skill documents — so the workflow, judgment rules, and
 safety constraints are identical.
 
+> **Tool availability**: invoking this skill (which you just did) makes the plugin's
+> `browser_*` tools available for the rest of the session — they are injected on
+> successful skill load. Until then they are deliberately hidden, so do not attempt
+> a browser action before loading this skill.
+
 ## Tool ↔ CLI map
 
 The tools below are thin, structured wrappers over the bsk CLI verbs of the same