feat: expand magic prompts coverage and split generation prompts (#835)

- Add configurable visible/instructions prompt families for commit/PR generation, PR checks/comments flows, and git conflict resolution helpers.
- Refactor prompt sending to explicit visible + synthetic parts instead of newline-based splitting, with legacy override migration for old keys.
- Polish Magic Prompts settings UX with grouped sidebar entries, tooltip-based descriptions, AI icon, and validation that visible prompts cannot be empty across web and VS Code runtimes.

packages/ui/src/components/session/GitHubIssuePickerDialog.tsx

@@ -29,6 +29,7 @@ import { useContextStore } from '@/stores/contextStore';
 import { useUIStore } from '@/stores/useUIStore';
 import { useGitHubAuthStore } from '@/stores/useGitHubAuthStore';
 import { opencodeClient } from '@/lib/opencode/client';
+import { renderMagicPrompt } from '@/lib/magicPrompts';
 import { createWorktreeSessionForNewBranch } from '@/lib/worktreeSessionCreator';
 import { generateBranchSlug } from '@/lib/git/branchNameGenerator';
 import type { GitHubIssue, GitHubIssueComment, GitHubIssuesListResult, GitHubIssueSummary } from '@/lib/api/types';
@@ -450,42 +451,10 @@ export function GitHubIssuePickerDialog({
         }
       }
 
-      const visiblePromptText = 'Review this issue using the provided issue context: title, body, labels, assignees, comments, metadata.';
-      const instructionsText = `Review this issue using the provided issue context.
-
-Process:
-- First classify the issue type (bug / feature request / question/support / refactor / ops) and state it as: Type: <one label>.
-- Gather any needed repository context (code, config, docs) to validate assumptions.
-- After gathering, if anything is still unclear or cannot be verified, do not speculate—state what’s missing and ask targeted questions.
-
-Output rules:
-- Compact output; pick ONE template below and omit the others.
-- No emojis. No code snippets. No fenced blocks.
-- Short inline code identifiers allowed.
-- Reference evidence with file paths and line ranges when applicable; if exact lines aren’t available, cite the file and say “approx” + why.
-- Keep the entire response under ~300 words.
-
-Templates (choose one):
-Bug:
-- Summary (1-2 sentences)
-- Likely cause (max 2)
-- Repro/diagnostics needed (max 3)
-- Fix approach (max 4 steps)
-- Verification (max 3)
-
-Feature:
-- Summary (1-2 sentences)
-- Requirements (max 4)
-- Unknowns/questions (max 4)
-- Proposed plan (max 5 steps)
-- Verification (max 3)
-
-Question/Support:
-- Summary (1-2 sentences)
-- Answer/guidance (max 6 lines)
-- Missing info (max 4)
-
-Do not implement changes until I confirm; end with: “Next actions: <1 sentence>”.`;
+      const visiblePromptText = await renderMagicPrompt('github.issue.review.visible', {
+        issue_number: String(issue.number),
+      });
+      const instructionsText = await renderMagicPrompt('github.issue.review.instructions');
       const contextText = buildIssueContextText({ repo: issueRes.repo, issue, comments });
 
       void opencodeClient.sendMessage({