Keep brand manual separate from repository internals

[vitormattos]

Audit follow-up after reviewing the LibreCode manual.

The LibreSign visual guidance itself is sound: the clear-space page already uses the reference E correctly, and the correct/incorrect-use page includes the rotated-logo and crowded-logo examples.

This PR fixes the content-boundary issues found during the audit:

• removes repository paths and internal filenames from user-facing manual prose;
• refers to official published files instead of implementation details;
• describes trademark policy without pointing readers to an internal Markdown filename;
• keeps GitHub only as a public source-files destination;
• corrects the README label: latest is a development build, not a stable released manual.

No LibreSign brand rule or visual identity is changed.

Every human-authored commit includes:

Signed-off-by: Vitor Mattos <vitor@php.rio>