fix(tmux): use tmux-256color and declare RGB per outer terminal

[ptaranat]

default-terminal was xterm-256color, a terminfo that describes something
tmux is not, so it misreported capabilities (e.g. italics) to programs in
the panes. Switch to tmux-256color, the entry that actually describes tmux.

tmux-256color does not advertise Tc/RGB on its own, so that switch alone
would have downgraded srcery's 24-bit colours to the 256-colour approximation
and stopped nvim matching the tmux status bar. terminal-features is keyed on
the OUTER terminal, so declare RGB for each one actually used (ghostty,
kitty), appended with -as to keep tmux's built-in feature table.

Verified in a fresh pane: TERM=tmux-256color, COLORTERM=truecolor, and a
24-bit escape emitted as 38;2;252;232;195 matching srcery #FCE8C3.

[ptaranat]

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• chore(config): trim comments across the tracked configs #11
• fix(tmux): use tmux-256color and declare RGB per outer terminal #10 👈 (View in Graphite)
• fix(zsh): restore PATH entries orphaned by ZDOTDIR #9 : 1 other dependent PR (#12 )
• fix(zsh): set PATH in .zshenv so early .zshrc consumers resolve #8
• main

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Pull request overview

This PR updates the tmux configuration to accurately report terminal capabilities inside tmux by switching the internal $TERM to tmux-256color, and restores truecolor (24-bit) support by explicitly declaring RGB capability per outer terminal.

Changes:

• Set tmux’s default-terminal to tmux-256color to avoid misreporting capabilities (e.g., italics) to applications inside panes.
• Append per-outer-terminal terminal-features entries to advertise truecolor (RGB) for xterm-ghostty and xterm-kitty.

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[ptaranat]

Reworked onto the current main and retargeted from fix/zsh-orbstack-jetbrains to main.

The original branch was cut before main was rewritten, so it predated the hyperlinks, extended-keys and focus-events settings that landed upstream in 6c30638. Rather than replace upstream's approach, this now combines both:

• default-terminal tmux-256color (from this branch) for correct capability reporting
• RGB declared for xterm-ghostty and xterm-kitty (this branch, covers the mac) and xterm-256color (upstream, covers Windows Terminal on WSL)
• upstream's hyperlinks, extended keys and focus events left untouched

The two fixes turned out to be complementary, not competing: terminal-features matches on the outer terminal's TERM, so upstream's xterm-256color:RGB line never matched under Ghostty on the mac.

Scope change worth a look: this also pins ncurses-term in .chezmoidata.yaml. Debian's ncurses-base does not ship the tmux-256color entry, so without it tmux would fail to start on the WSL box. macOS already has it.

Verified by loading the config on a scratch tmux socket: default-terminal resolves correctly and the three RGB features append to tmux's built-in feature table rather than replacing it.