Fix favicon and dashboard route 404s found in QA exploration

Problem

Investigate and fix the remaining favicon.ico 404 and the dashboard route-level 404 surfaced by qa-explore so console diagnostics are clean on the explored cloud flows.

Context

• QA exploration surfaced two remaining console/network issues on the cloud app:
• browsers still probed /favicon.ico and got a 404
• direct navigation to legacy dashboard URLs like /{org}/{project}/{dashboard_slug}/ returned Django's debug 404, because the canonical route now requires /d/{dashboard_slug}/
• The malformed dashboard path in the QA transcript was not emitted by the current UI templates; it came from a direct navigation attempt. That still warrants a compatibility fix so stale links and guessed URLs resolve cleanly instead of failing.
• The cloud base template already defined an inline SVG favicon, but browsers still made a fallback /favicon.ico request. The practical fix is to provide an explicit favicon asset and route-level handling.

Possible Solutions

• Add an explicit static favicon asset, reference it from the base template, and serve /favicon.ico via a redirect to that static asset.
• Recommended: small change, eliminates the console noise, and gives browsers a concrete fallback target.
• Add a project-level legacy dashboard redirect from /{org}/{project}/{dashboard_slug}/ to /{org}/{project}/d/{dashboard_slug}/.
• Recommended: preserves compatibility for stale links and QA/tooling guesses without changing the canonical URL structure.
• Ignore the legacy path because the current UI does not generate it.
• Rejected: the QA flow still hit it, and a clean redirect is low-risk.

Plan

1. Add a concrete favicon asset plus /favicon.ico handling in the cloud app.
2. Add a legacy dashboard redirect view/route that preserves query strings and forwards to the canonical dashboard_view.
3. Add focused cloud route smoke tests for both behaviors.
4. Run a QA verification pass against the local cloud URL and confirm the 404s are gone.

Implementation Progress

• Added apps/cloud/static/favicon.svg and updated apps/cloud/templates/base.html to use the static favicon for both icon and shortcut icon.
• Added a /favicon.ico route in apps/cloud/urls.py backed by a request-time redirect view so browser fallback probes resolve cleanly without import-time static URL resolution.
• Added dashboard_legacy_redirect in apps/cloud/apps/dashboards/views.py and wired it into apps/cloud/urls.py after the canonical project routes, preserving query strings while redirecting old-style dashboard URLs to /{org}/{project}/d/{dashboard_slug}/.
• Tightened the legacy redirect so it only fires for real dashboards; reserved slugs like charts and branches no longer get rewritten.
• Added focused smoke coverage in tests/cloud/test_cloud_route_smoke.py for:
• legacy dashboard URL redirect behavior
• favicon route redirect behavior
• project route non-shadowing for charts/ and branches/
• Focused validation passed: uv run pytest tests/cloud/test_cloud_route_smoke.py -q (8 passed).

QA Exploration

• Restarted the task worktree stack with just worktree-restart-serve and verified http://127.0.0.1:8100 was healthy.
• Ran the patched qa-explore wrapper from the active tooling task against this task worktree URL with focus on:
• favicon resolution
• legacy dashboard URL redirect behavior
• The verification artifact bundle is in /Users/dave.fowler/Fivetran/fix-qa-explore-delegated-run-stall-before-summary-handoff/.qa-explorer/runs/404-fix-verification.
• The recovered QA summary reported:
• no captured console errors
• no failed requests in the saved diagnostics
• The saved Playwright session confirmed the legacy route now redirects:
• GET /piedpiper/platform-analytics/adoption/ => 302

• followed by GET /piedpiper/platform-analytics/d/adoption/ => 200

• [x] QA exploration completed (or N/A for non-UI tasks)

Review Feedback

• Review flagged that the first legacy catch-all route could shadow charts/ and branches/. I moved the catch-all to the end of the project route list, added explicit smoke coverage for sibling routes, and tightened the redirect view to 404 when the slug is not a real dashboard.
• Review also flagged import-time static("favicon.svg") resolution in urls.py. I moved favicon handling into a request-time redirect view so the static URL is resolved lazily.
• [x] Review cleared