feat(shortener): public redirect + async click tracking + QR + analytics (B3-B4)

[PenguinzTech]

Feature (Track B, part 2) — redirect, tracking, QR, analytics

Stacked on #63 (base = feature/shortener-api). Targets release/v0.1.x.

• Redirect (app/redirect.py) — public GET /<short_code> → 302 to long_url (404 for unknown/inactive/expired); destination re-validated before redirect. Click tracking is non-blocking (asyncio.create_task after the response); click_count incremented atomically. link_clicks stores ip_hash (salted SHA256, never raw IP) + UA-parsed device/browser/os + referer.
• QR — GET /api/v1/urls/<id>/qr (auth + urls:read + tenant-scoped) returns an on-demand PNG of the short URL (qrcode+Pillow), not stored. Branded/color QR left as a Professional-tier TODO.
• Analytics (app/analytics.py) — /analytics/urls/<id> (per-link: total, clicks-by-day, top referers) and /analytics/summary (tenant totals, top links, time series), analytics:read + tenant-scoped. Basic tiers implemented; geo/device/browser breakdowns marked TODO(tiering) for the Enterprise advanced-analytics gate.
• deps: qrcode, Pillow, user-agents (pinned + hashed via uv).

Tests

619 passed, 90.66% coverage — redirect/404/expiry, async click + ip_hash (no raw IP), QR png bytes, analytics date-filter/pagination/tenant-isolation.

🤖 Generated with Claude Code

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	pypi/​user-agents@​2.2.0
	pypi/​ua-parser@​1.0.2
	pypi/​ua-parser-builtins@​202606

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[socket-security]

Warning

Review the following alerts detected in dependencies.

According to your organization's Security Policy, it is recommended to resolve "Warn" alerts. Learn more about Socket for GitHub.

Action	Severity	Alert  (click "▶" to expand/collapse)
Warn		Filesystem access: pypi ua-parser Location: Package overview From: services/flask-backend/requirements.txt → pypi/ua-parser@1.0.2 ℹ Read more on: This package | This alert | What is filesystem access? Next steps: Take a moment to review the security alert above. Review the linked package source code to understand the potential risk. Ensure the package is not malicious before proceeding. If you're unsure how to proceed, reach out to your security team or ask the Socket team for help at support@socket.dev. Suggestion: If a package must read the file system, clarify what it will read and ensure it reads only what it claims to. If appropriate, packages can leave file system access to consumers and operate on data passed to it instead. Mark the package as acceptable risk. To ignore this alert only in this pull request, reply with the comment @SocketSecurity ignore pypi/ua-parser@1.0.2. You can also ignore all packages with @SocketSecurity ignore-all. To ignore an alert for all future pull requests, use Socket's Dashboard to change the triage state of this alert.
Warn		Filesystem access: pypi user-agents Location: Package overview From: services/flask-backend/requirements.txt → pypi/user-agents@2.2.0 ℹ Read more on: This package | This alert | What is filesystem access? Next steps: Take a moment to review the security alert above. Review the linked package source code to understand the potential risk. Ensure the package is not malicious before proceeding. If you're unsure how to proceed, reach out to your security team or ask the Socket team for help at support@socket.dev. Suggestion: If a package must read the file system, clarify what it will read and ensure it reads only what it claims to. If appropriate, packages can leave file system access to consumers and operate on data passed to it instead. Mark the package as acceptable risk. To ignore this alert only in this pull request, reply with the comment @SocketSecurity ignore pypi/user-agents@2.2.0. You can also ignore all packages with @SocketSecurity ignore-all. To ignore an alert for all future pull requests, use Socket's Dashboard to change the triage state of this alert.
Warn		Unmaintained: pypi user-agents was last published 6 years ago Last Publish: 8/23/2020, 6:01:54 AM From: services/flask-backend/requirements.txt → pypi/user-agents@2.2.0 ℹ Read more on: This package | This alert | What are unmaintained packages? Next steps: Take a moment to review the security alert above. Review the linked package source code to understand the potential risk. Ensure the package is not malicious before proceeding. If you're unsure how to proceed, reach out to your security team or ask the Socket team for help at support@socket.dev. Suggestion: Package should publish periodic maintenance releases if they are maintained, or deprecate if they have no intention in further maintenance. Mark the package as acceptable risk. To ignore this alert only in this pull request, reply with the comment @SocketSecurity ignore pypi/user-agents@2.2.0. You can also ignore all packages with @SocketSecurity ignore-all. To ignore an alert for all future pull requests, use Socket's Dashboard to change the triage state of this alert.

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