Set up tab completion for the user instead of printing the script at them

Problem

Tab completion ships in v0.1.1 but nobody gets it without hand work:

• install.sh / install.ps1 wire PATH and WSO2_HOME only. The installer, README, install page and docs never mention completion.
• ws completion zsh typed in a terminal dumps ~200 lines of script. It reads as an error, and it does not say what to do with it.
• The manual steps have traps: plain zsh needs compinit first, and ~/.oh-my-zsh/completions/ does not exist by default, so the redirect fails.

What to build

1. ws completion install [shell]

Detects the shell from $SHELL when none is named. Supports zsh, bash, fish, powershell.

• zsh, bash: add source <(ws completion <shell>) inside the existing # >>> wso2 cli >>> … # <<< wso2 cli <<< profile block. Sourcing at start-up means the script never goes stale after a shell update.
• fish: write ~/.config/fish/completions/ws.fish.
• powershell: add ws completion powershell | Out-String | Invoke-Expression to $PROFILE.
• Idempotent: a second run changes nothing and says so.
• The command name comes from the build-time CLI name, not a literal ws.

Report, as a result (not raw prints):

Tab completion added for zsh.
Open a new terminal, then try: ws <TAB>

2. ws completion <shell> knows when it is on a terminal

• stdout piped or redirected: print the script, exactly as today. source <(ws completion zsh) must keep working.
• stdout is a TTY: print a short hint instead of the script, naming ws completion install, and --print to get the script anyway.

3. The installers set it up

• install.sh and install.ps1 run ws completion install after installing the binary, and the summary says "Tab completion added for ."
• WSO2_CLI_NO_PROFILE=1 skips it and prints the one manual line instead, the way it already does for PATH.
• A failure to set up completion is a warning, never a failed install.
• uninstall.sh already strips the profile block; it also has to remove the fish file. Same for uninstall.ps1.

4. Docs

A "Tab completion" section in the README and on the install page (scripts/site/index.html): the one command, and the per-shell manual line.

Where things are

• internal/app/completion.go: what completion offers (namespaces, product commands, flags, context names). The completion command itself is Cobra's default; it needs replacing or wrapping to add install, --print and the TTY check.
• scripts/install.sh: detect_profile, wire_path, remove_block, BLOCK_BEGIN / BLOCK_END, WSO2_CLI_NO_PROFILE (line ~400). scripts/uninstall.sh has the same block markers.
• Tests to extend: internal/app/completion_test.go, test/acceptance/install_unix_test.go, install_windows_test.go, uninstall_unix_test.go, uninstall_windows_test.go.

Decisions already made

• Profile line over a generated file for zsh and bash: never stale, costs ~20ms per new terminal.
• Completion of installed products needs nothing regenerated: the script asks ws __complete at Tab time, so ws product install is picked up at once.
• Piped output stays byte-for-byte what Cobra generates.

Open questions

• zsh without compinit in the profile: should install add autoload -U compinit && compinit inside the block, or detect it and tell the user? Adding it is friendlier; oh-my-zsh users already have it, and running it twice is slow.
• Should the profile edit live in Go (ws completion install) with the install scripts calling it, or stay in the scripts? One implementation in Go is preferred; confirm the scripts can rely on the freshly installed binary running on every supported platform.

Acceptance

• Fresh install on zsh and bash: new terminal, ws <TAB> lists commands, no manual step.
• ws completion zsh in a terminal prints the hint; ws completion zsh | head -1 prints #compdef ws.
• ws completion install twice leaves one line in the profile.
• Uninstall leaves no completion line or file behind.
• WSO2_CLI_NO_PROFILE=1 leaves every profile untouched.

Found while

Testing the real v0.1.1 install on macOS, zsh with oh-my-zsh. source <(ws completion zsh) typed into one session did not persist, and the documented-nowhere redirect failed on a missing directory.

Start with internal/app/completion.go and completion_test.go, then trace profile handling in scripts/install.sh and scripts/uninstall.sh. Run the listed install and uninstall acceptance tests while covering the shell-specific behavior, idempotence, TTY output, profile opt-out, and cleanup described in the acceptance criteria.