fix(ci): tune apt timeouts to fail fast on stalled CI mirror connections

[Wikid82]

Summary

The bash timeout/retry loop wrapping npx playwright install --with-deps (added in #1259 to stop apt hangs from burning the job's full 60-minute timeout) still lost all 3 retry attempts to the same degraded connection in a recent run (job):

12:14:24  Get:2 ... fonts-ipafont-gothic ... [3513 kB]
12:19:31  Get:3 ... fonts-freefont-ttf ... [5641 kB]   ← 5+ min for the next package to even start
12:24:16  timeout fires (10 min elapsed)

apt wasn't erroring or fully stalled with zero progress (the original bug #1259 fixed) — it was crawling at near-zero throughput on azure.archive.ubuntu.com. Since our outer retry loop doesn't change which connection/mirror apt uses, all 3 attempts hit the same degraded path and all 3 timed out, with no actual retry benefit.

Fix

Write an apt.conf.d drop-in before the first browser install in each of the 6 E2E jobs, setting:

Acquire::Retries "3";
Acquire::http::Timeout "15";
Acquire::https::Timeout "15";

This makes apt itself detect and abandon a stalled connection within 15s and retry against a fresh one, instead of sitting on one bad connection for the whole 10-minute outer budget — so the existing 3-attempt outer loop actually gets a chance to succeed against a different connection, rather than exhausting all 3 attempts on the same degraded path.

Test plan

• actionlint clean (including shellcheck validation of the embedded heredoc)
• Confirmed the YAML block-scalar indentation produces a correctly-terminated heredoc (parsed the actual script content via PyYAML to verify)
• lefthook run pre-commit clean

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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