feat: Tauri backend commands + wikipedia rewrite + github PR review pack

GUI integration
  - crates/jarvis-gui/src/tauri_commands/backends.rs — 5 new Tauri commands:
      get_active_backends()  -> {tts, llm, llm_model, profile}
      set_llm_backend(name)  -> swap LLM hot, persists to DB
      set_tts_backend(name)  -> persist choice (effective on jarvis-app restart)
      llm_reset_context()    -> clear conversation history
      llm_get_last_reply()   -> last assistant message or null
  - Registered in main.rs invoke_handler. Svelte side can now read active
    backend + swap from a settings page / footer without env-var gymnastics.

Wikipedia pack rewritten (resources/commands/wikipedia/)
  - Old `wiki/wiki.lua` (104 lines, hand-rolled Groq HTTP + inline SAPI PS) deleted.
  - Replacement `wikipedia/summary.lua` (87 lines):
    * REST summary endpoint (cleaner than opensearch+summary chain).
    * Russian first, English fallback with LLM translation.
    * Pure LLM fallback if Wikipedia has no article.
    * Uses jarvis.cmd.{ok,error,not_found} + jarvis.llm + jarvis.speak (no
      inline PowerShell SAPI). Phrases kept compatible with old pack.

GitHub PR voice review (resources/commands/github_pr/, 3 commands)
  - "текущий репо bossiara13/J.A.R.V.I.S-rust"  → github.set_repo
    Persists repo via jarvis.memory.
  - "какие пиары" / "открытые пиары"            → github.list_prs
    Calls `gh pr list --json number,title,author,createdAt --limit 10`.
    Parses count + first 3 titles by regex from JSON.
  - "разбери последний пиар" / "что в pr"       → github.summarize_pr
    `gh pr view N --json title,body,additions,deletions,changedFiles,author`,
    sends to LLM with "senior reviewer" system prompt, speaks 3-5 sentence
    review focusing on changes, risks, merge-readiness.
  - Requires gh CLI installed and `gh auth login` done.

Tests: 52/52 jarvis-core unit tests pass (Wikipedia pack TOML/script auto-checked).
Build: cargo build --release -p jarvis-app -p jarvis-gui green.

resources/commands/github_pr/summarize.lua

@@ -0,0 +1,62 @@
+local repo = jarvis.memory.recall("github.repo")
+if not repo or repo == "" then
+    return jarvis.cmd.not_found("Сначала укажите репозиторий: текущий репо owner/repo.")
+end
+
+-- get the most recent PR's number
+local list = jarvis.system.exec(string.format(
+    'gh pr list --repo "%s" --state open --json number --limit 1',
+    repo
+))
+if not list or not list.success then
+    return jarvis.cmd.error("gh CLI не отвечает.")
+end
+
+local number = (list.stdout or ""):match('"number"%s*:%s*(%d+)')
+if not number then
+    return jarvis.cmd.ok("Открытых пиаров нет.")
+end
+
+-- fetch title + body + diff stat
+local detail = jarvis.system.exec(string.format(
+    'gh pr view %s --repo "%s" --json title,body,additions,deletions,changedFiles,author',
+    number, repo
+))
+if not detail or not detail.success then
+    return jarvis.cmd.error("Не получилось получить PR.")
+end
+
+local d = detail.stdout or ""
+local title = d:match('"title"%s*:%s*"([^"]*)"') or "(no title)"
+local body  = d:match('"body"%s*:%s*"(.-)"') or ""
+body = body:gsub("\\n", "\n"):gsub("\\r", " "):gsub('\\"', '"'):gsub("\\\\", "\\")
+local additions = d:match('"additions"%s*:%s*(%d+)') or "?"
+local deletions = d:match('"deletions"%s*:%s*(%d+)') or "?"
+local files     = d:match('"changedFiles"%s*:%s*(%d+)') or "?"
+local author    = d:match('"login"%s*:%s*"([^"]*)"') or "(unknown)"
+
+-- Trim body for prompt
+if #body > 3000 then body = body:sub(1, 3000) .. "\n... [truncated]" end
+
+local user_prompt = string.format([[
+Repo: %s
+PR #%s: %s
+Author: %s
+Changed files: %s (+%s, -%s)
+Description:
+%s
+
+Кратко (3-5 предложений) на русском объясни: что меняет этот PR, какие риски, стоит ли мёржить.
+]], repo, number, title, author, files, additions, deletions, body)
+
+local review = jarvis.llm({
+    { role = "system", content = "Ты — старший разработчик, делаешь код-ревью. Отвечай по делу, без воды, без 'отличный PR' вступлений." },
+    { role = "user", content = user_prompt }
+}, { max_tokens = 400, temperature = 0.2 })
+
+if not review or review == "" then
+    return jarvis.cmd.error("Не получилось проанализировать.")
+end
+
+jarvis.system.notify(string.format("PR #%s — %s", number, title), review:sub(1, 250))
+return jarvis.cmd.ok(string.format("Пиар номер %s: %s", number, review))