feat: app tracker stats + list filtering (closes #40)

[laurentketterle-hub]

What

Adds application tracker enhancements for #40:

• nerajob app stats: status counts with visual bars, conversion funnel (applied→interview→offer→accepted), recent activity timeline
• nerajob app list --status <status>: filter applications by status (draft/applied/interview/offer/rejected/accepted)
• nerajob app list --sort-by <field>: sort by updated, created, status, or job_id
• Colored status output in list view

Tests

• 12 new tests: list filtering (5), stats display (4), status validation
• All tests use CliRunner with isolated temp directories

How to verify

# Stats summary
nerajob app stats

# Filter by status
nerajob app list --status applied
nerajob app list --status interview --sort-by created

Closes #40

[laurentketterle-hub]

/attempt 40

[laurentketterle-hub]

Friendly ping 👋 — this PR has been open for 3 days. Is there anything needed for review? Thanks!

[laurentketterle-hub]

/claim