Move do_render from internal procedure to module procedure in new
render_state_mod. This avoids gfortran trampolines that required
executable stack for callbacks.

- Remove -Wl,-z,noexecstack flag which crashes gfortran trampolines
- Add -fno-trampolines compiler flag (best practice)
- Fix unused argument suppression using c_associated() instead of transfer()
- gfortran requires executable stack for internal procedure callbacks (do_render)

- Remove unused parameter from dispatch_dec_private()
- Remove unused variable in dispatch_sgr()
- Add dummy references for unused GLFW callback arguments
- Mark selection_contains and selection_normalize as pure functions
- Add -Wl,-z,noexecstack linker flag to fix executable stack warning

- Skip rendering when window loses focus to prevent glfwSwapBuffers
  from blocking on Wayland frame callbacks
- Add glfwGetWindowAttrib binding and window_is_focused() function
- Track focus state to ensure initial render and clean unfocus state

- Replace glfwPollEvents with glfwWaitEventsTimeout for proper Wayland
  ping-pong handling when window is on inactive workspace
- Add desktop entry file for application launchers (wofi, rofi, etc.)
- Reduces CPU usage when terminal is idle

Load configuration at startup from ~/.config/fortty/fortty.toml:
- Apply color palette and default colors to cell module
- Use window dimensions from config
- Pass font path and size to renderer
- Use font metrics for cell dimensions instead of hardcoded values

Add config modules to CMakeLists.txt build.
Includes response handling in main loop for DA1/DSR replies.

Define config_t type with settings for:
- Window: width, height
- Font: path, fallback, size
- Colors: foreground, background, cursor, 16-color palette
- Terminal: scrollback lines
- Shell: program path

Implements config_load with XDG Base Directory support,
hex color parsing (#RRGGBB), and sensible defaults.

Simple TOML parser for fortty configuration files:
- Section parsing: [section]
- Key-value pairs: key = value
- String values with quote handling
- Integer and logical value parsing
- Comment and inline comment support

Provides toml_open, toml_get_string, toml_get_integer,
toml_get_logical for reading configuration values.

Add custom 16-color palette support:
- set_palette_color: override individual palette entries
- set_default_colors: set default foreground/background
- init_default_palette: initialize with VGA-style defaults

Modify color_from_index to use custom palette for indices 0-15,
allowing configuration-driven terminal theming.

Add response queue to terminal for escape sequence replies:
- terminal_queue_response: buffer response to send to PTY
- terminal_has_response: check for pending response
- terminal_get_response: retrieve and clear pending response

Implement DA1 (Primary Device Attributes) responding as VT102,
and DSR (Device Status Report) for status and cursor position.
Fixes fish shell warning about unanswered DA1 query.

Updates the main program to use the new font fallback system and
scrollback buffer rendering.

Font handling:
- Use fontconfig to find system monospace font
- Search for Nerd Font icons (U+E5FF, U+E0A0) then Font Awesome (U+F07B)
- Fall back to hardcoded paths if fontconfig unavailable
- Add TARGET attribute to renderer for proper pointer handling
- Fix dangling font pointer by reassigning atlas%font after creation

Scrollback rendering:
- Render from scrollback buffer when scroll_offset > 0
- Integrate with terminal scroll view functions
- Properly handle mixed scrollback/screen content

The terminal now properly displays:
- Unicode characters (❯, arrows, etc.)
- Nerd Font icons (eza --icons, powerline)
- Scrollable history with mouse wheel and Shift+PageUp/Down

Implements fallback font loading for glyphs missing from the primary
font. Uses fontconfig for portable font discovery, with hardcoded
paths as fallback.

Font module (font.f90):
- Add ft_face_fallback and has_fallback fields to font_t
- font_load_fallback() to load secondary font
- font_has_glyph() to check glyph existence
- font_render_glyph_with_fallback() tries fallback if primary lacks glyph
- font_find_monospace() and font_find_for_codepoint() via fontconfig

Atlas module (atlas.f90):
- Increase atlas size to 1024x1024 for Unicode support
- Add extended glyph cache (256 entries) with hash table
- On-demand loading for non-ASCII codepoints

C helpers (freetype_helpers.c):
- fortty_ft_has_glyph() for glyph existence check
- fortty_fc_find_font_for_char() finds font with specific codepoint
- fortty_fc_find_monospace_font() finds system monospace font

CMakeLists.txt:
- Link fontconfig when available, define HAVE_FONTCONFIG

Implements a 10,000 line scrollback buffer using a circular buffer
design. Users can scroll through terminal history.

New features:
- Circular buffer scrollback_mod with configurable capacity
- Mouse wheel scrolling (3 lines per notch)
- Shift+PageUp/PageDown for page-wise scrolling
- Auto-reset to live view on keyboard input

Files:
- scrollback.f90: New circular buffer implementation
- terminal.f90: Scrollback integration, scroll_offset tracking
- window.f90: Scroll callbacks, terminal pointer for scrolling
- glfw_bindings.f90: glfwSetScrollCallback binding

The parser now properly decodes UTF-8 multi-byte sequences instead of
passing raw bytes as codepoints. This fixes rendering of Unicode
characters like ❯ (U+276F) which were previously displayed incorrectly.

Changes:
- Add UTF-8 state machine with utf8_codepoint and utf8_remaining fields
- Handle 2-byte, 3-byte, and 4-byte UTF-8 sequences
- Properly detect and handle invalid continuation bytes
- Make handle_ground recursive for error recovery

- Add GLFW key constants and modifier masks
- Implement char callback for text input with UTF-8 encoding
- Implement key callback for special keys (arrows, F1-12, Home/End, etc.)
- Handle Ctrl+A through Ctrl+Z combinations
- Generate xterm-compatible escape sequences for special keys
- Connect PTY to window module for keyboard input
- Integrate parser into main loop

- Create parser.f90 with state machine (ground, escape, CSI, OSC states)
- Add CSI dispatch for cursor movement, erase, SGR colors/attributes
- Support 256-color palette and RGB colors in cell.f90
- Add DEC private modes (alternate screen, cursor visibility)
- Add terminal operations: save/restore cursor, scroll region,
  insert/delete lines/chars, reverse index, reset