## Summary
* **What is the goal of this PR?** fix edge case for definition
## Additional Context
If loadFromFile() returns false (no state file exists — first boot, or
SD missing), lastSleepImage is never set and contains garbage.
[SleepActivity.cpp:83] then uses it in a while comparison to avoid
repeating the same image. The JSON path (doc["lastSleepImage"] |
(uint8_t)0) handles it, but only if the file exists.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? _** NO **_
## Summary
**What is the goal of this PR?**
This change avoids the pattern of creating a `std::string` using
`.substr` in order to compare against a file extension literal.
```c++
std::string path;
if (path.length() >= 4 && path.substr(path.length() - 4) == ".ext")
```
The `checkFileExtension` utility has moved from StringUtils to
FsHelpers, to be available to code in lib/. The signature now accepts a
`std::string_view` instead of `std::string`, which makes the single
implementation reusable for Arduino `String`.
Added utility functions for commonly repeated extensions.
These changes **save about 2 KB of flash (5,999,427 to 5,997,343)**.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? _**NO**_
## Summary
* Custom sleep screen images now load from /.sleep directory
(preferred), falling back to /sleep for backwards compatibility. The
dot-prefix keeps the directory hidden from the file browser.
* Rewrote User Guide section 3.6 to document all six sleep screen modes,
cover settings, and the updated custom image setup.
## Additional Context
* The sleep directoy entry while browsing files was distracting.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? _NO_
jpirnay