fix: preserve literal < and > in playlist script output - #1343

Summary

Literal < and > characters now display in the playlist instead of being silently dropped. A title like <3 or a > b renders as written, with no need for the \< escape workaround.

Why this matters

The playlist runs script output through a second formatting pass, and ScriptFormatter treated every <...> sequence as a formatting tag (issue #1224). Unrecognised angle-bracket content was consumed and discarded. In src/gui/scripting/scriptformatter.cpp, formatBlock() now only enters tag processing when the text after < is a recognised formatter (via ScriptFormatterRegistry::isKnown) that closes with >; otherwise it emits the original <...> text verbatim. readTagContent() stops at a nested < so a literal < cannot swallow a following real tag, and angle detection checks the token value so the scanner keywords LESS/GREATER are not mistaken for bracket characters. Known tags with bad options still fall through to processFormat() and render their inner text.

Testing

Added cases to tests/gui/scriptformattertest.cpp covering literal brackets with spaces (a < b > c), I <3 this, an unknown tag kept literal (<notatag>rest), literal text mixed with real formatting (I <3 <b>this</b> and <b>I <3 this</b>), and the keyword words (<LESS>, 5 LESS than 6). Existing bold/italic/colour/link tests continue to assert no regression. The Qt6 toolchain is not installed in this environment, so the suite was not run here; clang-format passes on both files.

Fixes #1224