refactor(shell): modularize shell config into per-shell profiles and conf.d

Split bash config into dedicated aliases and profile files. Extract
fish shell init from config.fish into composable conf.d fragments
(setup, environment, ssh-auth-sock). Remove the generic profile in
favor of the bash-specific one. Add a static SSH_AUTH_SOCK symlink
so tmux sessions always see the current socket regardless of which
shell spawned them.

config/bash/aliases

@@ -0,0 +1,9 @@
+alias zero='zero.js'
+alias wtc="wt switch --create --execute=$EDITOR"
+alias wts="wt switch"
+alias wtr="wt remove @"
+alias ll="eza -l -g --icons"
+alias ls="eza -al --color=always --group-directories-first"
+alias g="git"
+alias neogit="nvim +Neogit"
+