Add Traefik for parallel development

[backspace]

This is a big undertaking and still in progress but promising!

• custom domain instead of localhost? was suggested earlier but Puppeteer blocked lvh.me so…
• cleanup of Synapse synapse-data-* directories?
• are host builds v slow?
• needing to run register-realm-users seems annoying
• probably macOS-centric at the moment
• what’s the deal with localhost:4205 realm(s)

[github-actions]

Preview deployments

• Host staging preview
• Host production preview

[github-actions]

Host Test Results

    1 files  ±  0      1 suites  ±0   1h 38m 40s ⏱️ - 13m 44s
1 811 tests  - 104  1 797 ✅  - 102  14 💤  - 1  0 ❌ ±0 
1 825 runs   - 105  1 811 ✅  - 102  14 💤  - 1  0 ❌  - 1 

Results for commit dcc047e. ± Comparison against base commit 079e239.

This pull request removes 104 tests.

Chrome ‑ Acceptance | code submode | schema editor tests: adding a "default" field type from the schema editor
Chrome ‑ Acceptance | code submode | schema editor tests: adding a field from schema editor - cardinality test
Chrome ‑ Acceptance | code submode | schema editor tests: adding a field from schema editor - whole flow test
Chrome ‑ Acceptance | code submode | schema editor tests: an empty file is detected
Chrome ‑ Acceptance | code submode | schema editor tests: can list the inheritance chain of a card with complex cyclic relationships
Chrome ‑ Acceptance | code submode | schema editor tests: card type and fields are clickable and navigate to the correct file
Chrome ‑ Acceptance | code submode | schema editor tests: deleting a field from schema editor
Chrome ‑ Acceptance | code submode | schema editor tests: editing a field from schema editor
Chrome ‑ Acceptance | code submode | schema editor tests: editing a local field from schema editor
Chrome ‑ Acceptance | code submode | schema editor tests: renaming a field from the schema editor
…

♻️ This comment has been updated with latest results.