fix(app): fix session file loading, shader linking, and menu flashing (#39)

[mcoliver]

Fixes #39

Summary of Changes

1. OpenGL Resource Sharing Across Contexts ():

   • Enabled Qt::AA_ShareOpenGLContexts before creating QApplication in src/bin/nsapps/UTV/main.cpp. On macOS, QTMetalVideoDevice creates an offscreen QOpenGLContext for rendering; without process-wide context sharing, static functions in IPCore (such as SourceRGBA) compiled in one context were invalid in another context, producing OpenGL linking errors:

     ERROR: compiling program:
     ERROR: with functions: SourceRGBA
     ERROR: No definition of SourceRGBA86f32ffb in fragment shader
     

   • Added a defensive check !glIsShader(F->state()->shader) in ShaderProgram.cpp to automatically release and recompile static shader functions if their handle is invalid in the current OpenGL context.

2. Prevent Session Files from Being Dispatched to Media Preloader:

   • In RvSession::LoadState, verified that file extensions are not .rv, .rvedl, or .edl before invoking m_session->startPreloadingMedia(filename).
   • Session files are GTO/EDL files loaded via session readers; passing them to the movie/image preloader caused brute-force reader probes.

3. Prevent NanoSVG False Positive Matching:

   • Removed BruteForceIO capability from IOsvg (cap = ImageRead) and added validation for g && g->shapes in IOsvg::getImageInfo. NanoSVG parses any text file as an empty SVG; without magic-byte verification, it was falsely claiming .rv files were SVG images and movie sequences.

4. Debounce Menu Rebuilding on Startup:

   • In RvDocument::notification, switched menuChangedMessage handling to call setBuildMenu() rather than immediately executing mergeMenu() synchronously.
   • Configured m_menuTimer as a single-shot timer. During startup, dozens of modes activate and fire invalidateMenu(); debouncing coalesces these into a single menu build and completely eliminates the rapid menu bar flashing.

5. Fix Console Log Mangling of <...>:

   • In RvConsoleWindow.cpp, escaped raw log text with toHtmlEscaped() when appending to HTML. Unescaped strings containing comparison operators (< and > in GLSL code or C++ templates) were previously stripped by Qt's rich text parser as unknown HTML tags.

6. Reuse Initial Empty Document on macOS File Open:

   • In RvApplication::newSessionFromFiles, checked if an existing document is currently open with no sources loaded. If so, incoming files from a macOS QFileOpenEvent are loaded directly into that session rather than creating an extra redundant window.

7. Apple Flex 2.6+ 64-bit Compatibility:

   • Updated cmake/macros/rv_lex.cmake to properly detect Apple flex on macOS.
   • Updated FlexLexer.h in both Gto and MuLang to use size_t for buffer sizes and ssize_t for LexerInput return types.