refactor(ocs): improve readability of v1 front controller

[joshtrichards]

Summary

This refactors ocs/v1.php to make the request flow easier to read without changing the endpoint's behavior. Somewhat inspired as an incremental counterpart to #60362 (and to some extent #60293).

What changed

• Introduced local variables for request path handling and bootstrapping state
• Made the maintenance/upgrade short-circuit more explicit
• Grouped request handling into clearer phases:
  • app bootstrap
  • request validation
  • login / update-path handling
  • route dispatch
• Kept the existing OCS exception-to-response mapping intact
• Simplified the generic error path by removing unnecessary nesting

Notes

• This is a readability-only cleanup
• No intended behavior changes
• /core/update remains the only bypass for the early maintenance/upgrade response

TODO

• Test test test

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI