Prompt user after upgrading to RDTS-enabled version

[luke-jr]

Require consensusrules=rdts in config to start; if missing, give a brief explanation and let the GUI user consent on the spot.

Intended to only be merged together with #238

[jlopp]

Concept ACK; it's very important to get explicit agreement from users regarding consensus changes.

[kwsantiago]

Return value of WriteSettingsFile() is silently discarded. If writing fails (disk full, permissions), the user's consent is lost and they'll be re-prompted on every startup despite having already consented. Should at least log a warning on failure.

[luke-jr]

WriteSettingsFile itself logs already?

[Copilot]

Pull request overview

This PR adds a user consent mechanism for the "Reduced Data Temporary Softfork" (RDTS) protocol change in Bitcoin Knots. On mainnet, the software requires the user to explicitly acknowledge the consensus rule change via the -consensusrules=rdts config option or an interactive GUI prompt before the node will start. This is designed to work alongside PR #238 which implements the actual RDTS deployment.

Changes:

• Added UserProtocolRulesConsent() in init.cpp that checks for consensusrules=rdts config, prompts GUI users interactively, and persists consent to settings.json
• Added rich-text URL linkification to all GUI ThreadSafeMessageBox/ThreadSafeQuestion messages using a new regex-based MakeHtmlLink overload, plus a <qt> prefix convention for rich text rendering
• Updated resetSettings() to preserve the consensus rules consent setting across GUI settings resets, and added the -consensusrules argument to available CLI options

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/init.cpp	Core consent logic: UserProtocolRulesConsent() function and its invocation during AppInitMain (skipped for test chains)
src/chainparamsbase.h	Defines CONSENSUSRULES_CONFIG_NAME and CONSENSUSRULES_REQUIRED constants
src/chainparamsbase.cpp	Registers -consensusrules CLI argument
src/qt/bitcoingui.cpp	Adds <qt> prefix-based rich text rendering and auto-linking of HTTPS URLs in all message boxes
src/qt/guiutil.h	Declares new MakeHtmlLink(const QString&) overload
src/qt/guiutil.cpp	Implements regex-based URL-to-HTML-link conversion for HTTPS URLs
src/node/interfaces.cpp	Preserves consensusrules setting during resetSettings() and adds chainparamsbase.h include
test/functional/mining_mainnet.py	Adds -consensusrules=rdts to mainnet test args
test/functional/rpc_validateaddress.py	Adds -consensusrules=rdts to mainnet test args

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