chore(types): enable strict backend type checking

[AlCalzone]

Enables strict backend and backend-test type checking as the final type-safety gate.

• Resolves remaining nullable and unknown-value boundaries without intended runtime changes.
• Adds non-vacuous server/test type checks to CI and locks the extracted module boundaries.
• Review focus: guards, defaults, and error paths that could accidentally alter compatibility.

Part of #4722. Stacked on #4735.

[coveralls]

Coverage Report for CI Build 29582065023

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No base build found for commit 7444653 on alcalzone-alcalzone-backend-refactor-node-projecti.
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Coverage: 62.995%

Details

• Patch coverage: 204 uncovered changes across 5 files (99 of 303 lines covered, 32.67%).

Uncovered Changes

File	Changed	Covered	%
api/lib/ZwaveClient.ts	179	50	27.93%
api/lib/Gateway.ts	82	22	26.83%
api/app.ts	23	12	52.17%
api/lib/ZnifferManager.ts	7	4	57.14%
api/lib/DebugManager.ts	4	3	75.0%
Total (7 files)	303	99	32.67%

Coverage Regressions

Requires a base build to compare against. How to fix this →

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Coverage Stats

Relevant Lines:	8568
Covered Lines:	5640
Line Coverage:	65.83%
Relevant Branches:	5203
Covered Branches:	3035
Branch Coverage:	58.33%
Branches in Coverage %:	Yes
Coverage Strength:	36.71 hits per line

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💛 - Coveralls