feat(tmux): auto-name sessions with emoji + codename

- scripts/tmux-session-name.sh: generates random emoji + adj-noun name
  40 emojis x 40 adjectives x 40 nouns = 64,000 combinations
  Only renames numerically-named sessions (skips explicit names)

- tmux.conf.local: session-created hook calls the script automatically

- shell/common: added DOTFILES=$HOME/dotfiles env var so hooks and
  scripts can find the dotfiles root without hardcoded paths

Examples: '🐉 sonic-oracle', '🌟 electric-nebula', '🔱 nova-comet'

tmux/.tmux.conf.local

@@ -366,6 +366,12 @@ source-file "/Users/jsarthak/dotfiles/tmux/config/keybindings.conf"
 
 setw -g window-status-separator " #[fg=#484848]• " #!important
 
+# ── Auto-name sessions (emoji + codename) ─────────────────────────────────────
+# Fires on every new session. Skips sessions the user explicitly named.
+# Script lives in ~/dotfiles/scripts/tmux-session-name.sh
+set-hook -g session-created \
+  'run-shell "bash $HOME/dotfiles/scripts/tmux-session-name.sh \"#{session_name}\" \"#{session_id}\""'
+
 # ── Mode indicator (always-on, Neovim-style) ──────────────────────────────────
 # NORMAL = working in tmux (default, always visible)
 # VISUAL = in copy-mode (prefix + Enter)