refactor: split views, reorganize CSS, add docs for new contributors

[gerardm27]

Summary

Structural refactor to make the codebase easier for new organizers. No logic changes, only code moved around hehe.

Views splitting

Six monolithic views.py files converted to views/ packages, split by feature concern:

App	Files
organizers	lists.py, review.py, batch_ops.py
applications	hacker.py, mentor.py, sponsor.py, draft.py
reimbursement	hacker.py, organizer.py
user	authentication.py, profile.py
baggage	hacker.py, volunteer.py
hardware	hacker.py, admin.py

CSS reorganization

• custom-bootstrap.css (was 1.5k lines) split into 14 component files under app/static/css/bootstrap-overrides/
• App-specific styles extracted from main.css into stats/static/css/stats.css and organizers/static/css/organizers.css

Documentation

New docs/ folder with four guides for new webdev organizers:

• docs/getting-started.md — what the app does, app-by-app overview, URL map, where templates and styles live
• docs/setting-up.md — local dev setup (extracted from README)
• docs/contributing.md — worked examples for the most common yearly changes (add/remove a form field, change the reimbursement cap)
• docs/email-templates.md — full table of every email the system sends, how to edit content and subjects, how to add template variables