feat(parallel): add Parallel as a bundled web_search provider (#85158)

- New extensions/parallel package modeled on extensions/exa
- Wires Parallel's POST /v1/search through the generic web_search contract,
  exposing Parallel's recommended {objective, search_queries} shape (plus
  optional count, session_id, client_model) so the model can supply both the
  natural-language goal and 2-3 short keyword queries as Parallel docs advise
- client_model lets the model report its own slug so Parallel can tailor
  optimizations for the consuming model's capabilities; partitions the cache
  by client_model so different models do not silently share ranked excerpts
- Honors top-level tools.web.search.{maxResults,timeoutSeconds,cacheTtlMinutes}
  via the shared SDK helpers (mergeScopedSearchConfig, withTrustedWebSearchEndpoint,
  buildSearchCacheKey, read/writeCachedSearchPayload)
- Auto-detect order 75; auth via PARALLEL_API_KEY or
  plugins.entries.parallel.config.webSearch.apiKey
- Optional baseUrl override for proxies (e.g. Cloudflare AI Gateway)
- Threads caller-supplied session_id through follow-up calls; strips
  auto-generated session_id from the shared cache to avoid cross-task leaks
- Always sends advanced_settings.max_results so result volume matches the
  OpenClaw web_search default (5) instead of Parallel's default (10)
- Identifies the plugin via User-Agent header built from package version
- Runtime accepts the generic `query` arg as a fallback so the operator
  CLI (openclaw capability web.search) keeps working when Parallel is the
  active provider: it is promoted into the lone `search_queries` entry.
  `objective` stays optional and is never synthesized from a keyword
  query (Parallel documents it as natural-language intent). Agent callers
  using the native objective+search_queries shape take precedence; the
  schema still advertises only the native keys
- Updates the agent tool-display extractor (src/agents/tool-display-common.ts)
  to recognize Parallel's objective+search_queries shape so calls render with
  query context in CLI progress and Codex activity metadata
- Adds /tools/parallel-search docs page, web.md provider listing, docs nav,
  labeler entry, per-plugin registration contract test, and minimal core
  touch-points (legacy migrate, registration cases, providers contract list,
  runtime bundled list, vitest extension paths)

docs/docs.json

@@ -1331,6 +1331,7 @@
                       "tools/kimi-search",
                       "tools/minimax-search",
                       "tools/ollama-search",
+                      "tools/parallel-search",
                       "tools/perplexity-search",
                       "tools/searxng-search",
                       "tools/tavily"