fix: online state, offline device delete, Node.js 26 tests, @iobroker/testing 6

[DutchmanNL]

Fixes the open online-state and device-delete bugs and the two repository-checker errors in #870, which are blocking the next stable update (#869).

Bug fixes

• Log voll seit letzter stable #788, online state not refreshing with 0.7.3 #794: _online written as text. When a device couldn't be initialised, getDeviceJSON passed { val: false, ack: true } to create_state, which wrote it as the string '{"val":false,"ack":true}'. js-controller then logged has to be type "boolean" but received type "string", which is visible in the logs posted in Log voll seit letzter stable #788. It now writes false and marks the device disconnected. This is based on fix online state #792 by @arteck (co-author). That PR has merge conflicts, so I carried over the fix rather than its maxRetries = 0 change, which belongs to the feature request add maxRetries per device #793.
• Log voll seit letzter stable #788: log spam. "Unable to initialise …" is now a warning once per outage. Later attempts for a device that stays offline are logged at debug level, and the flag resets once the device answers. This is what was asked for in the thread.
• Unable to delete offline device in V0.9.2 #787: offline devices could not be deleted. The deleteDevice message used this.devices[ip].name (the friendly name) as the object ID. Device objects are keyed by MAC address, and a device that has been offline since adapter start has no name in memory, so deletion always failed with Device with IP … not found. It now uses the MAC address and falls back to the device objects when the device isn't in memory. delDevice also accepts instance numbers above 9.
• README links to a document that is not in the repository #876: removed the README link to docs/DEPLOYMENT_SETUP.md, which doesn't exist and broke the iobroker.net docs build. A short paragraph about trusted publishing replaces it.

CI / repository checker

• E3025: the adapter-tests matrix now covers Node.js 22.x, 24.x and 26.x (Compatibility check and testing for node.js 26 #872). This is what bot PR [iobroker-bot] Update Node.js version range at test-and-release workflow to 22, 24 and 26 #873 does.
• E0036: @iobroker/testing goes from ^5.3.0 to ^6.3.0.
• W3009: the concurrency block now uses the form the checker expects; esphome and sourceanalytix already use it.
• Weekly duplicate issues: check-copilot-template.yml looked for open issues labelled copilot-setup and automation, but update issues are labelled template-update, so the check never found them and opened a new one every Sunday. It now matches on automation. I closed the 30 older duplicates and left 🤖 Update ioBroker Copilot Instructions Template #879 open.

Tests (local, Node 22)

• npm run lint: 0 errors (3 any warnings that were already there)
• test:js 1, test:package 59, test:unit 49 passing
• npm run test:integration: the adapter starts with @iobroker/testing 6

W3032 (the tag run for v0.9.2 failed) clears with the next successful release.

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