fix(vscode): harden extension commands with overwrite flows, shared PR service, and UX polish

[digitarald]

Summary

Hardens the VS Code extension with consistent error handling, overwrite confirmation flows, a shared local PR service, and several UX improvements.

Changes

Bug fixes

• Codicon rendering — $(check) / $(error) don't render in progress.report(), replaced with ✓ / ✗
• Swallowed errors — auto-analyze .catch(() => {}) now logs with console.error
• Generate overwrite — wrapped in try/catch to show "overwrite failed" instead of silently dropping

UX consistency

• Overwrite flows — init, generate, and instructions commands now try force: false first, prompt "Overwrite" when all files exist, and use force: true on confirmation — with dedicated try/catch in each
• File count in messages — all overwrite warnings now include the count ("All N files already exist")
• Judge model config — added primer.judgeModel setting (no default, falls back to primer.model)
• PR file picker — QuickPick with pre-selected Primer files before commit
• Empty-files guard — PR command warns with actionable message when no Primer files found

Architecture

• src/services/localPr.ts — extracted shared service for local PR workflows:
  • isPrimerFile() — pattern matching with Windows backslash normalization
  • detectGitHubRemote() — parse owner/repo from origin
  • getBranchInfo() — current + default branch (anchored origin/ regex)
  • getPrimerFilesFromStatus() — filtered git status
  • commitAndPush() — uses pushBranch() from git.ts for credential sanitization, accepts optional token
• Extension PR command refactored to use shared service (removed direct simple-git import)
• totalFiles / totalSkipped — instructions overwrite counts only areas with non-empty content

Tests

• 11 new tests for isPrimerFile covering exact matches, suffixes, rejection, substring, and Windows backslash paths
• All 275 tests pass, both typechecks clean