Add soft assertions (scoped accumulator, aggregate failures)

[JE-Chen]

assert_all takes a pre-built spec list up front — there was no scoped accumulator you sprinkle check() calls into across interleaved actions that raises everything on block exit (JUnit5 assertAll / Playwright expect.soft / AssertJ SoftAssertions).

• SoftAssertions context manager: check(condition, message) records pass/fail (never raises mid-block, returns the bool to branch on), check_equal shortcut, failures / passed accessors, assert_all() raises the aggregate. __exit__ calls assert_all on a clean exit and never masks an exception already propagating; raise_on_exit=False collects without auto-raising.
• AC_soft_assert aggregates a JSON checks list ({value, op, expected, message}, op = eq/ne/gt/lt/contains/truthy) → {ok, passed, failures}, reporting all failures; raise_on_fail to raise.
• Pure-stdlib; fully headless-testable. Wired through all 5 layers + headless test + EN/Zh docs + WHATS_NEW. Qt-free.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 33 complexity · 0 duplication

Metric	Results
Complexity	33
Duplication	0

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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