bug: duplicate company+role jobs cause silent data loss on delete/move

[creativereason]

Problem

PATCH and DELETE in app/api/jobs/route.ts (lines 74, 106) use findIndex to locate a job by company + role. If two jobs in the same section share the same company and role, only the first one is ever reachable — the second cannot be edited, moved, or deleted.

There is also no guard on the write path (POST) to prevent duplicate company+role pairs from being inserted in the first place.

Reproduction

1. Add two jobs with identical company and role to the same section (e.g. via direct edit of jobs.json or a scrape that returns the same listing twice)
2. Try to delete or move the second one — the first is always affected instead

Root cause

findIndex((j) => j.company === company && j.role === role) returns the first match. The composite key company::role (now via jobKey()) is not guaranteed unique within a section.

Options considered

• UUID per job — generate a stable id on insert, use it for all mutations. Blocks duplicate identity entirely. Requires schema change and migration.
• Block duplicates on insert — reject POST if jobKey(company, role) already exists in that section. Keeps findIndex safe but permanently prevents tracking two roles with identical titles at the same company.
• Index-based mutations — pass array index from client for delete/move. No schema change, but fragile under concurrent edits.

Proposed fix

Add to the slice backlog as a sequenced slice after the IJobRepository interface (Slice 5), since the right fix (UUID) touches the repository contract and all mutation paths.

Affected files

• app/api/jobs/route.ts — PATCH (line 74), DELETE (line 106)
• lib/jobs.ts — job types (no id field currently)
• app/page.tsx — all jobKey() call sites used as React keys and mutation identifiers