[Pipeline B] Apply routes → services → repositories layering to templates (#640, part 2)

[abhishek-8081]

Closes #640 (part 2 of 2 — part 1 was the forms layering in #652).

Applies the routes → services → repositories layering to the templates routes, same as part 1 did for forms.

• New TemplateService (app/services/template.py) holds the logic — PDF field extraction, file saving, and the per-endpoint orchestration — matching the FormService/InputService pattern.
• The two delete-dependency queries moved into repository functions (get_submissions_by_template, get_jobs_by_template).
• templates.py routes are now thin: parse → service → return. HTTP concerns (404s, file checks) stay in the route.
• Controller is unchanged — the service calls it, doesn't rewrite it.

Behavior is unchanged: 152 tests pass with only mock-location changes, no response-assertion changes. ruff check app/ is clean, and no direct DB queries remain in templates.py.

A couple of things I kept exactly as they were:

• The delete cascade still commits once at the end (atomic — a partial failure deletes nothing), rather than committing per row.
• The PDF field-extraction logic moved verbatim (same field ordering and type mapping).

Follow-up: _resolve_project_file / PROJECT_ROOT is now duplicated across forms.py, form.py, and template.py — worth a small consolidation issue later.