COLDCARD firmware

This commit only adds and updates test files for the COLDCARD firmware. It expands automated tests for temporary seed handling under a restricted 'hobble' mode, including a new test case for BIP-39 passphrases and a more complete XPRV import test. There are no changes to the actual firmware code that runs on the device, so this commit does not introduce or fix any security vulnerability by itself.

A developer added a comment in the COLDCARD MK4 bootloader code flagging that a function reads a configuration byte from a secure chip but does not check whether the read operation failed. If the read fails, the function could return an uninitialized or garbage value. This is a code-quality and potential security issue, but the patch only adds a comment—it does not fix the bug.

This commit only updates user documentation. It fixes a typo in a menu path and adds a new section explaining what to do if a user forgets their 'Bypass PIN' for the Spending Policy feature: perform a factory reset via 'Destroy Seed' and restore from backup. There is no code change and no security vulnerability is being fixed.

This commit fixes a small bug in the COLDCARD wallet's login security check. When the device asks the user to confirm the first and last seed words (to prove they know the backup), the old code could accidentally keep leftover words from a previous attempt. The change makes the word collection more reliable and adds a 'Startup...' message so the screen doesn't look frozen. It is a cleanup/hardening fix rather than a clear-cut exploitable vulnerability.

This commit adjusts how COLDCARD's 'hobbled mode' handles temporary seeds and the Seed Vault. Hobbled mode is a restricted operating mode (often tied to a special PIN or duress-like setup). The change makes temporary seeds read-only: users can import and use an existing temporary seed for signing, but cannot generate new words or save the temporary seed into the Seed Vault. It also exposes a 'Temporary Seed' menu under Advanced/Tools when a spending-policy flag called 'okeys' is enabled. The commit is titled 'testing' and appears to be a work-in-progress feature patch with added tests, not a published security fix.

This commit fixes a PIN-uniqueness check in the COLDCARD's 'Seed Vault / Secure Spending Policy' setup. Previously, when a user picked an unlock PIN, the code only compared it against the main PIN and visible 'trick' PINs, but missed hidden trick PINs. That could let the same PIN be used for two different security features, which can cause confusion or allow a hidden trick PIN to silently override the intended unlock behavior. The patch now asks the secure element (SE2) whether the PIN is already in use anywhere before accepting it.

This commit fixes the 'first and last seed word' login challenge on older COLDCARD Mk4 devices. Previously, the on-screen word picker for this security check was broken (the code even had a 'TODO: fix bugs here on Mk4' comment), which could have allowed someone with physical access to bypass or fail the word-check screen. The patch replaces the buggy callback-based picker with a working one, so the device can now properly verify the user's seed words during login.