Add bash shell completion support

[ryanfowler]

Implement the Shell interface for bash, adding tab completion via COMP_WORDS/COMPREPLY with -o nosort -o nospace flags. Update docs, install script, and CLI flag values to include bash alongside fish and zsh.

[Copilot]

Pull request overview

This PR adds bash shell completion support to the fetch CLI tool, implementing the Shell interface for bash alongside the existing fish and zsh implementations.

Changes:

• Implements Bash struct with Register() and Complete() methods using COMP_WORDS/COMPREPLY
• Adds "bash" as a valid value for the --complete flag
• Updates documentation and install script with bash completion instructions

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/complete/shells.go	Adds Bash struct implementing Shell interface with completion logic
internal/complete/complete_test.go	Adds comprehensive test cases for bash completion scenarios
internal/cli/cli_test.go	Adds test to verify flags are in alphabetical order
internal/cli/app.go	Reorders flags alphabetically and adds "bash" to --complete flag values
install.sh	Adds bash completion installation to .bashrc
docs/getting-started.md	Documents bash completion setup command
docs/cli-reference.md	Updates --complete flag documentation to include bash

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